HOWTO/man: improve descriptions of max open zones options

[fio.git] / HOWTO.rst

How fio works
-------------

The first step in getting fio to simulate a desired I/O workload, is writing a
job file describing that specific setup. A job file may contain any number of
threads and/or files -- the typical contents of the job file is a *global*
section defining shared parameters, and one or more job sections describing the
jobs involved. When run, fio parses this file and sets everything up as
described. If we break down a job from top to bottom, it contains the following
basic parameters:

`I/O type`_

                Defines the I/O pattern issued to the file(s).  We may only be reading
                sequentially from this file(s), or we may be writing randomly. Or even
                mixing reads and writes, sequentially or randomly.
                Should we be doing buffered I/O, or direct/raw I/O?

`Block size`_

                In how large chunks are we issuing I/O? This may be a single value,
                or it may describe a range of block sizes.

`I/O size`_

                How much data are we going to be reading/writing.

`I/O engine`_

                How do we issue I/O? We could be memory mapping the file, we could be
                using regular read/write, we could be using splice, async I/O, or even
                SG (SCSI generic sg).

`I/O depth`_

                If the I/O engine is async, how large a queuing depth do we want to
                maintain?


`Target file/device`_

                How many files are we spreading the workload over.

`Threads, processes and job synchronization`_

                How many threads or processes should we spread this workload over.

The above are the basic parameters defined for a workload, in addition there's a
multitude of parameters that modify other aspects of how this job behaves.


Command line options
--------------------

.. option:: --debug=type

        Enable verbose tracing `type` of various fio actions.  May be ``all`` for all types
        or individual types separated by a comma (e.g. ``--debug=file,mem`` will
        enable file and memory debugging).  Currently, additional logging is
        available for:

        *process*
                        Dump info related to processes.
        *file*
                        Dump info related to file actions.
        *io*
                        Dump info related to I/O queuing.
        *mem*
                        Dump info related to memory allocations.
        *blktrace*
                        Dump info related to blktrace setup.
        *verify*
                        Dump info related to I/O verification.
        *all*
                        Enable all debug options.
        *random*
                        Dump info related to random offset generation.
        *parse*
                        Dump info related to option matching and parsing.
        *diskutil*
                        Dump info related to disk utilization updates.
        *job:x*
                        Dump info only related to job number x.
        *mutex*
                        Dump info only related to mutex up/down ops.
        *profile*
                        Dump info related to profile extensions.
        *time*
                        Dump info related to internal time keeping.
        *net*
                        Dump info related to networking connections.
        *rate*
                        Dump info related to I/O rate switching.
        *compress*
                        Dump info related to log compress/decompress.
        *steadystate*
                        Dump info related to steadystate detection.
        *helperthread*
                        Dump info related to the helper thread.
        *zbd*
                        Dump info related to support for zoned block devices.
        *?* or *help*
                        Show available debug options.

.. option:: --parse-only

        Parse options only, don't start any I/O.

.. option:: --merge-blktrace-only

        Merge blktraces only, don't start any I/O.

.. option:: --output=filename

        Write output to file `filename`.

.. option:: --output-format=format

        Set the reporting `format` to `normal`, `terse`, `json`, or `json+`.  Multiple
        formats can be selected, separated by a comma.  `terse` is a CSV based
        format.  `json+` is like `json`, except it adds a full dump of the latency
        buckets.

.. option:: --bandwidth-log

        Generate aggregate bandwidth logs.

.. option:: --minimal

        Print statistics in a terse, semicolon-delimited format.

.. option:: --append-terse

        Print statistics in selected mode AND terse, semicolon-delimited format.
        **Deprecated**, use :option:`--output-format` instead to select multiple
        formats.

.. option:: --terse-version=version

        Set terse `version` output format (default 3, or 2 or 4 or 5).

.. option:: --version

        Print version information and exit.

.. option:: --help

        Print a summary of the command line options and exit.

.. option:: --cpuclock-test

        Perform test and validation of internal CPU clock.

.. option:: --crctest=[test]

        Test the speed of the built-in checksumming functions. If no argument is
        given, all of them are tested. Alternatively, a comma separated list can
        be passed, in which case the given ones are tested.

.. option:: --cmdhelp=command

        Print help information for `command`. May be ``all`` for all commands.

.. option:: --enghelp=[ioengine[,command]]

        List all commands defined by `ioengine`, or print help for `command`
        defined by `ioengine`.  If no `ioengine` is given, list all
        available ioengines.

.. option:: --showcmd

        Convert given job files to a set of command-line options.

.. option:: --readonly

        Turn on safety read-only checks, preventing writes and trims.  The
        ``--readonly`` option is an extra safety guard to prevent users from
        accidentally starting a write or trim workload when that is not desired.
        Fio will only modify the device under test if
        `rw=write/randwrite/rw/randrw/trim/randtrim/trimwrite` is given.  This
        safety net can be used as an extra precaution.

.. option:: --eta=when

        Specifies when real-time ETA estimate should be printed.  `when` may be
        `always`, `never` or `auto`. `auto` is the default, it prints ETA
        when requested if the output is a TTY. `always` disregards the output
        type, and prints ETA when requested. `never` never prints ETA.

.. option:: --eta-interval=time

        By default, fio requests client ETA status roughly every second. With
        this option, the interval is configurable. Fio imposes a minimum
        allowed time to avoid flooding the console, less than 250 msec is
        not supported.

.. option:: --eta-newline=time

        Force a new line for every `time` period passed.  When the unit is omitted,
        the value is interpreted in seconds.

.. option:: --status-interval=time

        Force a full status dump of cumulative (from job start) values at `time`
        intervals. This option does *not* provide per-period measurements. So
        values such as bandwidth are running averages. When the time unit is omitted,
        `time` is interpreted in seconds. Note that using this option with
        ``--output-format=json`` will yield output that technically isn't valid
        json, since the output will be collated sets of valid json. It will need
        to be split into valid sets of json after the run.

.. option:: --section=name

        Only run specified section `name` in job file.  Multiple sections can be specified.
        The ``--section`` option allows one to combine related jobs into one file.
        E.g. one job file could define light, moderate, and heavy sections. Tell
        fio to run only the "heavy" section by giving ``--section=heavy``
        command line option.  One can also specify the "write" operations in one
        section and "verify" operation in another section.  The ``--section`` option
        only applies to job sections.  The reserved *global* section is always
        parsed and used.

.. option:: --alloc-size=kb

        Allocate additional internal smalloc pools of size `kb` in KiB.  The
        ``--alloc-size`` option increases shared memory set aside for use by fio.
        If running large jobs with randommap enabled, fio can run out of memory.
        Smalloc is an internal allocator for shared structures from a fixed size
        memory pool and can grow to 16 pools. The pool size defaults to 16MiB.

        NOTE: While running :file:`.fio_smalloc.*` backing store files are visible
        in :file:`/tmp`.

.. option:: --warnings-fatal

        All fio parser warnings are fatal, causing fio to exit with an
        error.

.. option:: --max-jobs=nr

        Set the maximum number of threads/processes to support to `nr`.
        NOTE: On Linux, it may be necessary to increase the shared-memory
        limit (:file:`/proc/sys/kernel/shmmax`) if fio runs into errors while
        creating jobs.

.. option:: --server=args

        Start a backend server, with `args` specifying what to listen to.
        See `Client/Server`_ section.

.. option:: --daemonize=pidfile

        Background a fio server, writing the pid to the given `pidfile` file.

.. option:: --client=hostname

        Instead of running the jobs locally, send and run them on the given `hostname`
        or set of `hostname`\s.  See `Client/Server`_ section.

.. option:: --remote-config=file

        Tell fio server to load this local `file`.

.. option:: --idle-prof=option

        Report CPU idleness. `option` is one of the following:

                **calibrate**
                        Run unit work calibration only and exit.

                **system**
                        Show aggregate system idleness and unit work.

                **percpu**
                        As **system** but also show per CPU idleness.

.. option:: --inflate-log=log

        Inflate and output compressed `log`.

.. option:: --trigger-file=file

        Execute trigger command when `file` exists.

.. option:: --trigger-timeout=time

        Execute trigger at this `time`.

.. option:: --trigger=command

        Set this `command` as local trigger.

.. option:: --trigger-remote=command

        Set this `command` as remote trigger.

.. option:: --aux-path=path

        Use the directory specified by `path` for generated state files instead
        of the current working directory.

Any parameters following the options will be assumed to be job files, unless
they match a job file parameter. Multiple job files can be listed and each job
file will be regarded as a separate group. Fio will :option:`stonewall`
execution between each group.


Job file format
---------------

As previously described, fio accepts one or more job files describing what it is
supposed to do. The job file format is the classic ini file, where the names
enclosed in [] brackets define the job name. You are free to use any ASCII name
you want, except *global* which has special meaning.  Following the job name is
a sequence of zero or more parameters, one per line, that define the behavior of
the job. If the first character in a line is a ';' or a '#', the entire line is
discarded as a comment.

A *global* section sets defaults for the jobs described in that file. A job may
override a *global* section parameter, and a job file may even have several
*global* sections if so desired. A job is only affected by a *global* section
residing above it.

The :option:`--cmdhelp` option also lists all options. If used with a `command`
argument, :option:`--cmdhelp` will detail the given `command`.

See the `examples/` directory for inspiration on how to write job files.  Note
the copyright and license requirements currently apply to `examples/` files.

So let's look at a really simple job file that defines two processes, each
randomly reading from a 128MiB file:

.. code-block:: ini

    ; -- start job file --
    [global]
    rw=randread
    size=128m

    [job1]

    [job2]

    ; -- end job file --

As you can see, the job file sections themselves are empty as all the described
parameters are shared. As no :option:`filename` option is given, fio makes up a
`filename` for each of the jobs as it sees fit. On the command line, this job
would look as follows::

$ fio --name=global --rw=randread --size=128m --name=job1 --name=job2


Let's look at an example that has a number of processes writing randomly to
files:

.. code-block:: ini

    ; -- start job file --
    [random-writers]
    ioengine=libaio
    iodepth=4
    rw=randwrite
    bs=32k
    direct=0
    size=64m
    numjobs=4
    ; -- end job file --

Here we have no *global* section, as we only have one job defined anyway.  We
want to use async I/O here, with a depth of 4 for each file. We also increased
the buffer size used to 32KiB and define numjobs to 4 to fork 4 identical
jobs. The result is 4 processes each randomly writing to their own 64MiB
file. Instead of using the above job file, you could have given the parameters
on the command line. For this case, you would specify::

$ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4

When fio is utilized as a basis of any reasonably large test suite, it might be
desirable to share a set of standardized settings across multiple job files.
Instead of copy/pasting such settings, any section may pull in an external
:file:`filename.fio` file with *include filename* directive, as in the following
example::

    ; -- start job file including.fio --
    [global]
    filename=/tmp/test
    filesize=1m
    include glob-include.fio

    [test]
    rw=randread
    bs=4k
    time_based=1
    runtime=10
    include test-include.fio
    ; -- end job file including.fio --

.. code-block:: ini

    ; -- start job file glob-include.fio --
    thread=1
    group_reporting=1
    ; -- end job file glob-include.fio --

.. code-block:: ini

    ; -- start job file test-include.fio --
    ioengine=libaio
    iodepth=4
    ; -- end job file test-include.fio --

Settings pulled into a section apply to that section only (except *global*
section). Include directives may be nested in that any included file may contain
further include directive(s). Include files may not contain [] sections.


Environment variables
~~~~~~~~~~~~~~~~~~~~~

Fio also supports environment variable expansion in job files. Any sub-string of
the form ``${VARNAME}`` as part of an option value (in other words, on the right
of the '='), will be expanded to the value of the environment variable called
`VARNAME`.  If no such environment variable is defined, or `VARNAME` is the
empty string, the empty string will be substituted.

As an example, let's look at a sample fio invocation and job file::

$ SIZE=64m NUMJOBS=4 fio jobfile.fio

.. code-block:: ini

    ; -- start job file --
    [random-writers]
    rw=randwrite
    size=${SIZE}
    numjobs=${NUMJOBS}
    ; -- end job file --

This will expand to the following equivalent job file at runtime:

.. code-block:: ini

    ; -- start job file --
    [random-writers]
    rw=randwrite
    size=64m
    numjobs=4
    ; -- end job file --

Fio ships with a few example job files, you can also look there for inspiration.

Reserved keywords
~~~~~~~~~~~~~~~~~

Additionally, fio has a set of reserved keywords that will be replaced
internally with the appropriate value. Those keywords are:

**$pagesize**

        The architecture page size of the running system.

**$mb_memory**

        Megabytes of total memory in the system.

**$ncpus**

        Number of online available CPUs.

These can be used on the command line or in the job file, and will be
automatically substituted with the current system values when the job is
run. Simple math is also supported on these keywords, so you can perform actions
like::

        size=8*$mb_memory

and get that properly expanded to 8 times the size of memory in the machine.


Job file parameters
-------------------

This section describes in details each parameter associated with a job.  Some
parameters take an option of a given type, such as an integer or a
string. Anywhere a numeric value is required, an arithmetic expression may be
used, provided it is surrounded by parentheses. Supported operators are:

        - addition (+)
        - subtraction (-)
        - multiplication (*)
        - division (/)
        - modulus (%)
        - exponentiation (^)

For time values in expressions, units are microseconds by default. This is
different than for time values not in expressions (not enclosed in
parentheses). The following types are used:


Parameter types
~~~~~~~~~~~~~~~

**str**
        String: A sequence of alphanumeric characters.

**time**
        Integer with possible time suffix.  Without a unit value is interpreted as
        seconds unless otherwise specified.  Accepts a suffix of 'd' for days, 'h' for
        hours, 'm' for minutes, 's' for seconds, 'ms' (or 'msec') for milliseconds and
        'us' (or 'usec') for microseconds.  For example, use 10m for 10 minutes.

.. _int:

**int**
        Integer. A whole number value, which may contain an integer prefix
        and an integer suffix:

        [*integer prefix*] **number** [*integer suffix*]

        The optional *integer prefix* specifies the number's base. The default
        is decimal. *0x* specifies hexadecimal.

        The optional *integer suffix* specifies the number's units, and includes an
        optional unit prefix and an optional unit.  For quantities of data, the
        default unit is bytes. For quantities of time, the default unit is seconds
        unless otherwise specified.

        With :option:`kb_base`\=1000, fio follows international standards for unit
        prefixes.  To specify power-of-10 decimal values defined in the
        International System of Units (SI):

                * *K* -- means kilo (K) or 1000
                * *M* -- means mega (M) or 1000**2
                * *G* -- means giga (G) or 1000**3
                * *T* -- means tera (T) or 1000**4
                * *P* -- means peta (P) or 1000**5

        To specify power-of-2 binary values defined in IEC 80000-13:

                * *Ki* -- means kibi (Ki) or 1024
                * *Mi* -- means mebi (Mi) or 1024**2
                * *Gi* -- means gibi (Gi) or 1024**3
                * *Ti* -- means tebi (Ti) or 1024**4
                * *Pi* -- means pebi (Pi) or 1024**5

        For Zone Block Device Mode:
                * *z*  -- means Zone

        With :option:`kb_base`\=1024 (the default), the unit prefixes are opposite
        from those specified in the SI and IEC 80000-13 standards to provide
        compatibility with old scripts.  For example, 4k means 4096.

        For quantities of data, an optional unit of 'B' may be included
        (e.g., 'kB' is the same as 'k').

        The *integer suffix* is not case sensitive (e.g., m/mi mean mebi/mega,
        not milli). 'b' and 'B' both mean byte, not bit.

        Examples with :option:`kb_base`\=1000:

                * *4 KiB*: 4096, 4096b, 4096B, 4ki, 4kib, 4kiB, 4Ki, 4KiB
                * *1 MiB*: 1048576, 1mi, 1024ki
                * *1 MB*: 1000000, 1m, 1000k
                * *1 TiB*: 1099511627776, 1ti, 1024gi, 1048576mi
                * *1 TB*: 1000000000, 1t, 1000m, 1000000k

        Examples with :option:`kb_base`\=1024 (default):

                * *4 KiB*: 4096, 4096b, 4096B, 4k, 4kb, 4kB, 4K, 4KB
                * *1 MiB*: 1048576, 1m, 1024k
                * *1 MB*: 1000000, 1mi, 1000ki
                * *1 TiB*: 1099511627776, 1t, 1024g, 1048576m
                * *1 TB*: 1000000000, 1ti, 1000mi, 1000000ki

        To specify times (units are not case sensitive):

                * *D* -- means days
                * *H* -- means hours
                * *M* -- means minutes
                * *s* -- or sec means seconds (default)
                * *ms* -- or *msec* means milliseconds
                * *us* -- or *usec* means microseconds

        If the option accepts an upper and lower range, use a colon ':' or
        minus '-' to separate such values. See :ref:`irange <irange>`.
        If the lower value specified happens to be larger than the upper value
        the two values are swapped.

.. _bool:

**bool**
        Boolean. Usually parsed as an integer, however only defined for
        true and false (1 and 0).

.. _irange:

**irange**
        Integer range with suffix. Allows value range to be given, such as
        1024-4096. A colon may also be used as the separator, e.g. 1k:4k. If the
        option allows two sets of ranges, they can be specified with a ',' or '/'
        delimiter: 1k-4k/8k-32k. Also see :ref:`int <int>`.

**float_list**
        A list of floating point numbers, separated by a ':' character.

With the above in mind, here follows the complete list of fio job parameters.


Units
~~~~~

.. option:: kb_base=int

        Select the interpretation of unit prefixes in input parameters.

                **1000**
                        Inputs comply with IEC 80000-13 and the International
                        System of Units (SI). Use:

                                - power-of-2 values with IEC prefixes (e.g., KiB)
                                - power-of-10 values with SI prefixes (e.g., kB)

                **1024**
                        Compatibility mode (default).  To avoid breaking old scripts:

                                - power-of-2 values with SI prefixes
                                - power-of-10 values with IEC prefixes

        See :option:`bs` for more details on input parameters.

        Outputs always use correct prefixes.  Most outputs include both
        side-by-side, like::

                bw=2383.3kB/s (2327.4KiB/s)

        If only one value is reported, then kb_base selects the one to use:

                **1000** -- SI prefixes

                **1024** -- IEC prefixes

.. option:: unit_base=int

        Base unit for reporting.  Allowed values are:

        **0**
                Use auto-detection (default).
        **8**
                Byte based.
        **1**
                Bit based.


Job description
~~~~~~~~~~~~~~~

.. option:: name=str

        ASCII name of the job. This may be used to override the name printed by fio
        for this job. Otherwise the job name is used. On the command line this
        parameter has the special purpose of also signaling the start of a new job.

.. option:: description=str

        Text description of the job. Doesn't do anything except dump this text
        description when this job is run. It's not parsed.

.. option:: loops=int

        Run the specified number of iterations of this job. Used to repeat the same
        workload a given number of times. Defaults to 1.

.. option:: numjobs=int

        Create the specified number of clones of this job. Each clone of job
        is spawned as an independent thread or process. May be used to setup a
        larger number of threads/processes doing the same thing. Each thread is
        reported separately; to see statistics for all clones as a whole, use
        :option:`group_reporting` in conjunction with :option:`new_group`.
        See :option:`--max-jobs`.  Default: 1.


Time related parameters
~~~~~~~~~~~~~~~~~~~~~~~

.. option:: runtime=time

        Tell fio to terminate processing after the specified period of time.  It
        can be quite hard to determine for how long a specified job will run, so
        this parameter is handy to cap the total runtime to a given time.  When
        the unit is omitted, the value is interpreted in seconds.

.. option:: time_based

        If set, fio will run for the duration of the :option:`runtime` specified
        even if the file(s) are completely read or written. It will simply loop over
        the same workload as many times as the :option:`runtime` allows.

.. option:: startdelay=irange(time)

        Delay the start of job for the specified amount of time.  Can be a single
        value or a range.  When given as a range, each thread will choose a value
        randomly from within the range.  Value is in seconds if a unit is omitted.

.. option:: ramp_time=time

        If set, fio will run the specified workload for this amount of time before
        logging any performance numbers. Useful for letting performance settle
        before logging results, thus minimizing the runtime required for stable
        results. Note that the ``ramp_time`` is considered lead in time for a job,
        thus it will increase the total runtime if a special timeout or
        :option:`runtime` is specified.  When the unit is omitted, the value is
        given in seconds.

.. option:: clocksource=str

        Use the given clocksource as the base of timing. The supported options are:

                **gettimeofday**
                        :manpage:`gettimeofday(2)`

                **clock_gettime**
                        :manpage:`clock_gettime(2)`

                **cpu**
                        Internal CPU clock source

        cpu is the preferred clocksource if it is reliable, as it is very fast (and
        fio is heavy on time calls). Fio will automatically use this clocksource if
        it's supported and considered reliable on the system it is running on,
        unless another clocksource is specifically set. For x86/x86-64 CPUs, this
        means supporting TSC Invariant.

.. option:: gtod_reduce=bool

        Enable all of the :manpage:`gettimeofday(2)` reducing options
        (:option:`disable_clat`, :option:`disable_slat`, :option:`disable_bw_measurement`) plus
        reduce precision of the timeout somewhat to really shrink the
        :manpage:`gettimeofday(2)` call count. With this option enabled, we only do
        about 0.4% of the :manpage:`gettimeofday(2)` calls we would have done if all
        time keeping was enabled.

.. option:: gtod_cpu=int

        Sometimes it's cheaper to dedicate a single thread of execution to just
        getting the current time. Fio (and databases, for instance) are very
        intensive on :manpage:`gettimeofday(2)` calls. With this option, you can set
        one CPU aside for doing nothing but logging current time to a shared memory
        location. Then the other threads/processes that run I/O workloads need only
        copy that segment, instead of entering the kernel with a
        :manpage:`gettimeofday(2)` call. The CPU set aside for doing these time
        calls will be excluded from other uses. Fio will manually clear it from the
        CPU mask of other jobs.


Target file/device
~~~~~~~~~~~~~~~~~~

.. option:: directory=str

        Prefix filenames with this directory. Used to place files in a different
        location than :file:`./`.  You can specify a number of directories by
        separating the names with a ':' character. These directories will be
        assigned equally distributed to job clones created by :option:`numjobs` as
        long as they are using generated filenames. If specific `filename(s)` are
        set fio will use the first listed directory, and thereby matching the
        `filename` semantic (which generates a file for each clone if not
        specified, but lets all clones use the same file if set).

        See the :option:`filename` option for information on how to escape "``:``"
        characters within the directory path itself.

        Note: To control the directory fio will use for internal state files
        use :option:`--aux-path`.

.. option:: filename=str

        Fio normally makes up a `filename` based on the job name, thread number, and
        file number (see :option:`filename_format`). If you want to share files
        between threads in a job or several
        jobs with fixed file paths, specify a `filename` for each of them to override
        the default. If the ioengine is file based, you can specify a number of files
        by separating the names with a ':' colon. So if you wanted a job to open
        :file:`/dev/sda` and :file:`/dev/sdb` as the two working files, you would use
        ``filename=/dev/sda:/dev/sdb``. This also means that whenever this option is
        specified, :option:`nrfiles` is ignored. The size of regular files specified
        by this option will be :option:`size` divided by number of files unless an
        explicit size is specified by :option:`filesize`.

        Each colon in the wanted path must be escaped with a ``\``
        character.  For instance, if the path is :file:`/dev/dsk/foo@3,0:c` then you
        would use ``filename=/dev/dsk/foo@3,0\:c`` and if the path is
        :file:`F:\\filename` then you would use ``filename=F\:\filename``.

        On Windows, disk devices are accessed as :file:`\\\\.\\PhysicalDrive0` for
        the first device, :file:`\\\\.\\PhysicalDrive1` for the second etc.
        Note: Windows and FreeBSD prevent write access to areas
        of the disk containing in-use data (e.g. filesystems).

        The filename "`-`" is a reserved name, meaning *stdin* or *stdout*.  Which
        of the two depends on the read/write direction set.

.. option:: filename_format=str

        If sharing multiple files between jobs, it is usually necessary to have fio
        generate the exact names that you want. By default, fio will name a file
        based on the default file format specification of
        :file:`jobname.jobnumber.filenumber`. With this option, that can be
        customized. Fio will recognize and replace the following keywords in this
        string:

                **$jobname**
                                The name of the worker thread or process.
                **$clientuid**
                                IP of the fio process when using client/server mode.
                **$jobnum**
                                The incremental number of the worker thread or process.
                **$filenum**
                                The incremental number of the file for that worker thread or
                                process.

        To have dependent jobs share a set of files, this option can be set to have
        fio generate filenames that are shared between the two. For instance, if
        :file:`testfiles.$filenum` is specified, file number 4 for any job will be
        named :file:`testfiles.4`. The default of :file:`$jobname.$jobnum.$filenum`
        will be used if no other format specifier is given.

        If you specify a path then the directories will be created up to the
        main directory for the file.  So for example if you specify
        ``filename_format=a/b/c/$jobnum`` then the directories a/b/c will be
        created before the file setup part of the job.  If you specify
        :option:`directory` then the path will be relative that directory,
        otherwise it is treated as the absolute path.

.. option:: unique_filename=bool

        To avoid collisions between networked clients, fio defaults to prefixing any
        generated filenames (with a directory specified) with the source of the
        client connecting. To disable this behavior, set this option to 0.

.. option:: opendir=str

        Recursively open any files below directory `str`.

.. option:: lockfile=str

        Fio defaults to not locking any files before it does I/O to them. If a file
        or file descriptor is shared, fio can serialize I/O to that file to make the
        end result consistent. This is usual for emulating real workloads that share
        files. The lock modes are:

                **none**
                        No locking. The default.
                **exclusive**
                        Only one thread or process may do I/O at a time, excluding all
                        others.
                **readwrite**
                        Read-write locking on the file. Many readers may
                        access the file at the same time, but writes get exclusive access.

.. option:: nrfiles=int

        Number of files to use for this job. Defaults to 1. The size of files
        will be :option:`size` divided by this unless explicit size is specified by
        :option:`filesize`. Files are created for each thread separately, and each
        file will have a file number within its name by default, as explained in
        :option:`filename` section.


.. option:: openfiles=int

        Number of files to keep open at the same time. Defaults to the same as
        :option:`nrfiles`, can be set smaller to limit the number simultaneous
        opens.

.. option:: file_service_type=str

        Defines how fio decides which file from a job to service next. The following
        types are defined:

                **random**
                        Choose a file at random.

                **roundrobin**
                        Round robin over opened files. This is the default.

                **sequential**
                        Finish one file before moving on to the next. Multiple files can
                        still be open depending on :option:`openfiles`.

                **zipf**
                        Use a *Zipf* distribution to decide what file to access.

                **pareto**
                        Use a *Pareto* distribution to decide what file to access.

                **normal**
                        Use a *Gaussian* (normal) distribution to decide what file to
                        access.

                **gauss**
                        Alias for normal.

        For *random*, *roundrobin*, and *sequential*, a postfix can be appended to
        tell fio how many I/Os to issue before switching to a new file. For example,
        specifying ``file_service_type=random:8`` would cause fio to issue
        8 I/Os before selecting a new file at random. For the non-uniform
        distributions, a floating point postfix can be given to influence how the
        distribution is skewed. See :option:`random_distribution` for a description
        of how that would work.

.. option:: ioscheduler=str

        Attempt to switch the device hosting the file to the specified I/O scheduler
        before running.

.. option:: create_serialize=bool

        If true, serialize the file creation for the jobs.  This may be handy to
        avoid interleaving of data files, which may greatly depend on the filesystem
        used and even the number of processors in the system.  Default: true.

.. option:: create_fsync=bool

        :manpage:`fsync(2)` the data file after creation. This is the default.

.. option:: create_on_open=bool

        If true, don't pre-create files but allow the job's open() to create a file
        when it's time to do I/O.  Default: false -- pre-create all necessary files
        when the job starts.

.. option:: create_only=bool

        If true, fio will only run the setup phase of the job.  If files need to be
        laid out or updated on disk, only that will be done -- the actual job contents
        are not executed.  Default: false.

.. option:: allow_file_create=bool

        If true, fio is permitted to create files as part of its workload.  If this
        option is false, then fio will error out if
        the files it needs to use don't already exist. Default: true.

.. option:: allow_mounted_write=bool

        If this isn't set, fio will abort jobs that are destructive (e.g. that write)
        to what appears to be a mounted device or partition. This should help catch
        creating inadvertently destructive tests, not realizing that the test will
        destroy data on the mounted file system. Note that some platforms don't allow
        writing against a mounted device regardless of this option. Default: false.

.. option:: pre_read=bool

        If this is given, files will be pre-read into memory before starting the
        given I/O operation. This will also clear the :option:`invalidate` flag,
        since it is pointless to pre-read and then drop the cache. This will only
        work for I/O engines that are seek-able, since they allow you to read the
        same data multiple times. Thus it will not work on non-seekable I/O engines
        (e.g. network, splice). Default: false.

.. option:: unlink=bool

        Unlink the job files when done. Not the default, as repeated runs of that
        job would then waste time recreating the file set again and again. Default:
        false.

.. option:: unlink_each_loop=bool

        Unlink job files after each iteration or loop.  Default: false.

.. option:: zonemode=str

        Accepted values are:

                **none**
                                The :option:`zonerange`, :option:`zonesize`,
                                :option `zonecapacity` and option:`zoneskip`
                                parameters are ignored.
                **strided**
                                I/O happens in a single zone until
                                :option:`zonesize` bytes have been transferred.
                                After that number of bytes has been
                                transferred processing of the next zone
                                starts. :option `zonecapacity` is ignored.
                **zbd**
                                Zoned block device mode. I/O happens
                                sequentially in each zone, even if random I/O
                                has been selected. Random I/O happens across
                                all zones instead of being restricted to a
                                single zone. The :option:`zoneskip` parameter
                                is ignored. :option:`zonerange` and
                                :option:`zonesize` must be identical.
                                Trim is handled using a zone reset operation.
                                Trim only considers non-empty sequential write
                                required and sequential write preferred zones.

.. option:: zonerange=int

        Size of a single zone. See also :option:`zonesize` and
        :option:`zoneskip`.

.. option:: zonesize=int

        For :option:`zonemode` =strided, this is the number of bytes to
        transfer before skipping :option:`zoneskip` bytes. If this parameter
        is smaller than :option:`zonerange` then only a fraction of each zone
        with :option:`zonerange` bytes will be accessed.  If this parameter is
        larger than :option:`zonerange` then each zone will be accessed
        multiple times before skipping to the next zone.

        For :option:`zonemode` =zbd, this is the size of a single zone. The
        :option:`zonerange` parameter is ignored in this mode.


.. option:: zonecapacity=int

        For :option:`zonemode` =zbd, this defines the capacity of a single zone,
        which is the accessible area starting from the zone start address.
        This parameter only applies when using :option:`zonemode` =zbd in
        combination with regular block devices. If not specified it defaults to
        the zone size. If the target device is a zoned block device, the zone
        capacity is obtained from the device information and this option is
        ignored.

.. option:: zoneskip=int

        For :option:`zonemode` =strided, the number of bytes to skip after
        :option:`zonesize` bytes of data have been transferred. This parameter
        must be zero for :option:`zonemode` =zbd.

.. option:: read_beyond_wp=bool

        This parameter applies to :option:`zonemode` =zbd only.

        Zoned block devices are block devices that consist of multiple zones.
        Each zone has a type, e.g. conventional or sequential. A conventional
        zone can be written at any offset that is a multiple of the block
        size. Sequential zones must be written sequentially. The position at
        which a write must occur is called the write pointer. A zoned block
        device can be either drive managed, host managed or host aware. For
        host managed devices the host must ensure that writes happen
        sequentially. Fio recognizes host managed devices and serializes
        writes to sequential zones for these devices.

        If a read occurs in a sequential zone beyond the write pointer then
        the zoned block device will complete the read without reading any data
        from the storage medium. Since such reads lead to unrealistically high
        bandwidth and IOPS numbers fio only reads beyond the write pointer if
        explicitly told to do so. Default: false.

.. option:: max_open_zones=int

        A zone of a zoned block device is in the open state when it is partially
        written (i.e. not all sectors of the zone have been written). Zoned
        block devices may have a limit on the total number of zones that can
        be simultaneously in the open state, that is, the number of zones that
        can be written to simultaneously. The :option:`max_open_zones` parameter
        limits the number of zones to which write commands are issued by all fio
        jobs, that is, limits the number of zones that will be in the open
        state. This parameter is relevant only if the :option:`zonemode` =zbd is
        used. The default value is always equal to maximum number of open zones
        of the target zoned block device and a value higher than this limit
        cannot be specified by users unless the option
        :option:`ignore_zone_limits` is specified. When
        :option:`ignore_zone_limits` is specified or the target device has no
        limit on the number of zones that can be in an open state,
        :option:`max_open_zones` can specify 0 to disable any limit on the
        number of zones that can be simultaneously written to by all jobs.

.. option:: job_max_open_zones=int

        In the same manner as :option:`max_open_zones`, limit the number of open
        zones per fio job, that is, the number of zones that a single job can
        simultaneously write to. A value of zero indicates no limit.
        Default: zero.

.. option:: ignore_zone_limits=bool

        If this option is used, fio will ignore the maximum number of open
        zones limit of the zoned block device in use, thus allowing the
        option :option:`max_open_zones` value to be larger than the device
        reported limit. Default: false.

.. option:: zone_reset_threshold=float

        A number between zero and one that indicates the ratio of logical
        blocks with data to the total number of logical blocks in the test
        above which zones should be reset periodically.

.. option:: zone_reset_frequency=float

        A number between zero and one that indicates how often a zone reset
        should be issued if the zone reset threshold has been exceeded. A zone
        reset is submitted after each (1 / zone_reset_frequency) write
        requests. This and the previous parameter can be used to simulate
        garbage collection activity.


I/O type
~~~~~~~~

.. option:: direct=bool

        If value is true, use non-buffered I/O. This is usually O_DIRECT. Note that
        OpenBSD and ZFS on Solaris don't support direct I/O.  On Windows the synchronous
        ioengines don't support direct I/O.  Default: false.

.. option:: atomic=bool

        If value is true, attempt to use atomic direct I/O. Atomic writes are
        guaranteed to be stable once acknowledged by the operating system. Only
        Linux supports O_ATOMIC right now.

.. option:: buffered=bool

        If value is true, use buffered I/O. This is the opposite of the
        :option:`direct` option. Defaults to true.

.. option:: readwrite=str, rw=str

        Type of I/O pattern. Accepted values are:

                **read**
                                Sequential reads.
                **write**
                                Sequential writes.
                **trim**
                                Sequential trims (Linux block devices and SCSI
                                character devices only).
                **randread**
                                Random reads.
                **randwrite**
                                Random writes.
                **randtrim**
                                Random trims (Linux block devices and SCSI
                                character devices only).
                **rw,readwrite**
                                Sequential mixed reads and writes.
                **randrw**
                                Random mixed reads and writes.
                **trimwrite**
                                Sequential trim+write sequences. Blocks will be trimmed first,
                                then the same blocks will be written to. So if ``io_size=64K``
                                is specified, Fio will trim a total of 64K bytes and also
                                write 64K bytes on the same trimmed blocks. This behaviour
                                will be consistent with ``number_ios`` or other Fio options
                                limiting the total bytes or number of I/O's.
                **randtrimwrite**
                                Like trimwrite, but uses random offsets rather
                                than sequential writes.

        Fio defaults to read if the option is not specified.  For the mixed I/O
        types, the default is to split them 50/50.  For certain types of I/O the
        result may still be skewed a bit, since the speed may be different.

        It is possible to specify the number of I/Os to do before getting a new
        offset by appending ``:<nr>`` to the end of the string given.  For a
        random read, it would look like ``rw=randread:8`` for passing in an offset
        modifier with a value of 8. If the suffix is used with a sequential I/O
        pattern, then the *<nr>* value specified will be **added** to the generated
        offset for each I/O turning sequential I/O into sequential I/O with holes.
        For instance, using ``rw=write:4k`` will skip 4k for every write.  Also see
        the :option:`rw_sequencer` option.

.. option:: rw_sequencer=str

        If an offset modifier is given by appending a number to the ``rw=<str>``
        line, then this option controls how that number modifies the I/O offset
        being generated. Accepted values are:

                **sequential**
                        Generate sequential offset.
                **identical**
                        Generate the same offset.

        ``sequential`` is only useful for random I/O, where fio would normally
        generate a new random offset for every I/O. If you append e.g. 8 to randread,
        you would get a new random offset for every 8 I/Os. The result would be a
        seek for only every 8 I/Os, instead of for every I/O. Use ``rw=randread:8``
        to specify that. As sequential I/O is already sequential, setting
        ``sequential`` for that would not result in any differences.  ``identical``
        behaves in a similar fashion, except it sends the same offset 8 number of
        times before generating a new offset.

.. option:: unified_rw_reporting=str

        Fio normally reports statistics on a per data direction basis, meaning that
        reads, writes, and trims are accounted and reported separately. This option
        determines whether fio reports the results normally, summed together, or as
        both options.
        Accepted values are:

                **none**
                        Normal statistics reporting.

                **mixed**
                        Statistics are summed per data direction and reported together.

                **both**
                        Statistics are reported normally, followed by the mixed statistics.

                **0**
                        Backward-compatible alias for **none**.

                **1**
                        Backward-compatible alias for **mixed**.

                **2**
                        Alias for **both**.

.. option:: randrepeat=bool

        Seed the random number generator used for random I/O patterns in a
        predictable way so the pattern is repeatable across runs. Default: true.

.. option:: allrandrepeat=bool

        Seed all random number generators in a predictable way so results are
        repeatable across runs.  Default: false.

.. option:: randseed=int

        Seed the random number generators based on this seed value, to be able to
        control what sequence of output is being generated.  If not set, the random
        sequence depends on the :option:`randrepeat` setting.

.. option:: fallocate=str

        Whether pre-allocation is performed when laying down files.
        Accepted values are:

                **none**
                        Do not pre-allocate space.

                **native**
                        Use a platform's native pre-allocation call but fall back to
                        **none** behavior if it fails/is not implemented.

                **posix**
                        Pre-allocate via :manpage:`posix_fallocate(3)`.

                **keep**
                        Pre-allocate via :manpage:`fallocate(2)` with
                        FALLOC_FL_KEEP_SIZE set.

                **truncate**
                        Extend file to final size via :manpage:`ftruncate(2)`
                        instead of allocating.

                **0**
                        Backward-compatible alias for **none**.

                **1**
                        Backward-compatible alias for **posix**.

        May not be available on all supported platforms. **keep** is only available
        on Linux. If using ZFS on Solaris this cannot be set to **posix**
        because ZFS doesn't support pre-allocation. Default: **native** if any
        pre-allocation methods except **truncate** are available, **none** if not.

        Note that using **truncate** on Windows will interact surprisingly
        with non-sequential write patterns. When writing to a file that has
        been extended by setting the end-of-file information, Windows will
        backfill the unwritten portion of the file up to that offset with
        zeroes before issuing the new write. This means that a single small
        write to the end of an extended file will stall until the entire
        file has been filled with zeroes.

.. option:: fadvise_hint=str

        Use :manpage:`posix_fadvise(2)` or :manpage:`posix_fadvise(2)` to
        advise the kernel on what I/O patterns are likely to be issued.
        Accepted values are:

                **0**
                        Backwards-compatible hint for "no hint".

                **1**
                        Backwards compatible hint for "advise with fio workload type". This
                        uses **FADV_RANDOM** for a random workload, and **FADV_SEQUENTIAL**
                        for a sequential workload.

                **sequential**
                        Advise using **FADV_SEQUENTIAL**.

                **random**
                        Advise using **FADV_RANDOM**.

.. option:: write_hint=str

        Use :manpage:`fcntl(2)` to advise the kernel what life time to expect
        from a write. Only supported on Linux, as of version 4.13. Accepted
        values are:

                **none**
                        No particular life time associated with this file.

                **short**
                        Data written to this file has a short life time.

                **medium**
                        Data written to this file has a medium life time.

                **long**
                        Data written to this file has a long life time.

                **extreme**
                        Data written to this file has a very long life time.

        The values are all relative to each other, and no absolute meaning
        should be associated with them.

.. option:: offset=int

        Start I/O at the provided offset in the file, given as either a fixed size in
        bytes, zones or a percentage. If a percentage is given, the generated offset will be
        aligned to the minimum ``blocksize`` or to the value of ``offset_align`` if
        provided. Data before the given offset will not be touched. This
        effectively caps the file size at `real_size - offset`. Can be combined with
        :option:`size` to constrain the start and end range of the I/O workload.
        A percentage can be specified by a number between 1 and 100 followed by '%',
        for example, ``offset=20%`` to specify 20%. In ZBD mode, value can be set as
        number of zones using 'z'.

.. option:: offset_align=int

        If set to non-zero value, the byte offset generated by a percentage ``offset``
        is aligned upwards to this value. Defaults to 0 meaning that a percentage
        offset is aligned to the minimum block size.

.. option:: offset_increment=int

        If this is provided, then the real offset becomes `offset + offset_increment
        * thread_number`, where the thread number is a counter that starts at 0 and
        is incremented for each sub-job (i.e. when :option:`numjobs` option is
        specified). This option is useful if there are several jobs which are
        intended to operate on a file in parallel disjoint segments, with even
        spacing between the starting points. Percentages can be used for this option.
        If a percentage is given, the generated offset will be aligned to the minimum
        ``blocksize`` or to the value of ``offset_align`` if provided. In ZBD mode, value can
        also be set as number of zones using 'z'.

.. option:: number_ios=int

        Fio will normally perform I/Os until it has exhausted the size of the region
        set by :option:`size`, or if it exhaust the allocated time (or hits an error
        condition). With this setting, the range/size can be set independently of
        the number of I/Os to perform. When fio reaches this number, it will exit
        normally and report status. Note that this does not extend the amount of I/O
        that will be done, it will only stop fio if this condition is met before
        other end-of-job criteria.

.. option:: fsync=int

        If writing to a file, issue an :manpage:`fsync(2)` (or its equivalent) of
        the dirty data for every number of blocks given. For example, if you give 32
        as a parameter, fio will sync the file after every 32 writes issued. If fio is
        using non-buffered I/O, we may not sync the file. The exception is the sg
        I/O engine, which synchronizes the disk cache anyway. Defaults to 0, which
        means fio does not periodically issue and wait for a sync to complete. Also
        see :option:`end_fsync` and :option:`fsync_on_close`.

.. option:: fdatasync=int

        Like :option:`fsync` but uses :manpage:`fdatasync(2)` to only sync data and
        not metadata blocks. In Windows, DragonFlyBSD or OSX there is no
        :manpage:`fdatasync(2)` so this falls back to using :manpage:`fsync(2)`.
        Defaults to 0, which means fio does not periodically issue and wait for a
        data-only sync to complete.

.. option:: write_barrier=int

        Make every `N-th` write a barrier write.

.. option:: sync_file_range=str:int

        Use :manpage:`sync_file_range(2)` for every `int` number of write
        operations. Fio will track range of writes that have happened since the last
        :manpage:`sync_file_range(2)` call. `str` can currently be one or more of:

                **wait_before**
                        SYNC_FILE_RANGE_WAIT_BEFORE
                **write**
                        SYNC_FILE_RANGE_WRITE
                **wait_after**
                        SYNC_FILE_RANGE_WAIT_AFTER

        So if you do ``sync_file_range=wait_before,write:8``, fio would use
        ``SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE`` for every 8
        writes. Also see the :manpage:`sync_file_range(2)` man page.  This option is
        Linux specific.

.. option:: overwrite=bool

        If true, writes to a file will always overwrite existing data. If the file
        doesn't already exist, it will be created before the write phase begins. If
        the file exists and is large enough for the specified write phase, nothing
        will be done. Default: false.

.. option:: end_fsync=bool

        If true, :manpage:`fsync(2)` file contents when a write stage has completed.
        Default: false.

.. option:: fsync_on_close=bool

        If true, fio will :manpage:`fsync(2)` a dirty file on close.  This differs
        from :option:`end_fsync` in that it will happen on every file close, not
        just at the end of the job.  Default: false.

.. option:: rwmixread=int

        Percentage of a mixed workload that should be reads. Default: 50.

.. option:: rwmixwrite=int

        Percentage of a mixed workload that should be writes. If both
        :option:`rwmixread` and :option:`rwmixwrite` is given and the values do not
        add up to 100%, the latter of the two will be used to override the
        first. This may interfere with a given rate setting, if fio is asked to
        limit reads or writes to a certain rate.  If that is the case, then the
        distribution may be skewed. Default: 50.

.. option:: random_distribution=str:float[:float][,str:float][,str:float]

        By default, fio will use a completely uniform random distribution when asked
        to perform random I/O. Sometimes it is useful to skew the distribution in
        specific ways, ensuring that some parts of the data is more hot than others.
        fio includes the following distribution models:

                **random**
                                Uniform random distribution

                **zipf**
                                Zipf distribution

                **pareto**
                                Pareto distribution

                **normal**
                                Normal (Gaussian) distribution

                **zoned**
                                Zoned random distribution

                **zoned_abs**
                                Zone absolute random distribution

        When using a **zipf** or **pareto** distribution, an input value is also
        needed to define the access pattern. For **zipf**, this is the `Zipf
        theta`. For **pareto**, it's the `Pareto power`. Fio includes a test
        program, :command:`fio-genzipf`, that can be used visualize what the given input
        values will yield in terms of hit rates.  If you wanted to use **zipf** with
        a `theta` of 1.2, you would use ``random_distribution=zipf:1.2`` as the
        option. If a non-uniform model is used, fio will disable use of the random
        map. For the **normal** distribution, a normal (Gaussian) deviation is
        supplied as a value between 0 and 100.

        The second, optional float is allowed for **pareto**, **zipf** and **normal** distributions.
        It allows one to set base of distribution in non-default place, giving more control
        over most probable outcome. This value is in range [0-1] which maps linearly to
        range of possible random values.
        Defaults are: random for **pareto** and **zipf**, and 0.5 for **normal**.
        If you wanted to use **zipf** with a `theta` of 1.2 centered on 1/4 of allowed value range,
        you would use ``random_distribution=zipf:1.2:0.25``.

        For a **zoned** distribution, fio supports specifying percentages of I/O
        access that should fall within what range of the file or device. For
        example, given a criteria of:

                * 60% of accesses should be to the first 10%
                * 30% of accesses should be to the next 20%
                * 8% of accesses should be to the next 30%
                * 2% of accesses should be to the next 40%

        we can define that through zoning of the random accesses. For the above
        example, the user would do::

                random_distribution=zoned:60/10:30/20:8/30:2/40

        A **zoned_abs** distribution works exactly like the **zoned**, except
        that it takes absolute sizes. For example, let's say you wanted to
        define access according to the following criteria:

                * 60% of accesses should be to the first 20G
                * 30% of accesses should be to the next 100G
                * 10% of accesses should be to the next 500G

        we can define an absolute zoning distribution with:

                random_distribution=zoned_abs=60/20G:30/100G:10/500g

        For both **zoned** and **zoned_abs**, fio supports defining up to
        256 separate zones.

        Similarly to how :option:`bssplit` works for setting ranges and
        percentages of block sizes. Like :option:`bssplit`, it's possible to
        specify separate zones for reads, writes, and trims. If just one set
        is given, it'll apply to all of them. This goes for both **zoned**
        **zoned_abs** distributions.

.. option:: percentage_random=int[,int][,int]

        For a random workload, set how big a percentage should be random. This
        defaults to 100%, in which case the workload is fully random. It can be set
        from anywhere from 0 to 100.  Setting it to 0 would make the workload fully
        sequential. Any setting in between will result in a random mix of sequential
        and random I/O, at the given percentages.  Comma-separated values may be
        specified for reads, writes, and trims as described in :option:`blocksize`.

.. option:: norandommap

        Normally fio will cover every block of the file when doing random I/O. If
        this option is given, fio will just get a new random offset without looking
        at past I/O history. This means that some blocks may not be read or written,
        and that some blocks may be read/written more than once. If this option is
        used with :option:`verify` and multiple blocksizes (via :option:`bsrange`),
        only intact blocks are verified, i.e., partially-overwritten blocks are
        ignored.  With an async I/O engine and an I/O depth > 1, it is possible for
        the same block to be overwritten, which can cause verification errors.  Either
        do not use norandommap in this case, or also use the lfsr random generator.

.. option:: softrandommap=bool

        See :option:`norandommap`. If fio runs with the random block map enabled and
        it fails to allocate the map, if this option is set it will continue without
        a random block map. As coverage will not be as complete as with random maps,
        this option is disabled by default.

.. option:: random_generator=str

        Fio supports the following engines for generating I/O offsets for random I/O:

                **tausworthe**
                        Strong 2^88 cycle random number generator.
                **lfsr**
                        Linear feedback shift register generator.
                **tausworthe64**
                        Strong 64-bit 2^258 cycle random number generator.

        **tausworthe** is a strong random number generator, but it requires tracking
        on the side if we want to ensure that blocks are only read or written
        once. **lfsr** guarantees that we never generate the same offset twice, and
        it's also less computationally expensive. It's not a true random generator,
        however, though for I/O purposes it's typically good enough. **lfsr** only
        works with single block sizes, not with workloads that use multiple block
        sizes. If used with such a workload, fio may read or write some blocks
        multiple times. The default value is **tausworthe**, unless the required
        space exceeds 2^32 blocks. If it does, then **tausworthe64** is
        selected automatically.


Block size
~~~~~~~~~~

.. option:: blocksize=int[,int][,int], bs=int[,int][,int]

        The block size in bytes used for I/O units. Default: 4096.  A single value
        applies to reads, writes, and trims.  Comma-separated values may be
        specified for reads, writes, and trims.  A value not terminated in a comma
        applies to subsequent types.

        Examples:

                **bs=256k**
                        means 256k for reads, writes and trims.

                **bs=8k,32k**
                        means 8k for reads, 32k for writes and trims.

                **bs=8k,32k,**
                        means 8k for reads, 32k for writes, and default for trims.

                **bs=,8k**
                        means default for reads, 8k for writes and trims.

                **bs=,8k,**
                        means default for reads, 8k for writes, and default for trims.

.. option:: blocksize_range=irange[,irange][,irange], bsrange=irange[,irange][,irange]

        A range of block sizes in bytes for I/O units.  The issued I/O unit will
        always be a multiple of the minimum size, unless
        :option:`blocksize_unaligned` is set.

        Comma-separated ranges may be specified for reads, writes, and trims as
        described in :option:`blocksize`.

        Example: ``bsrange=1k-4k,2k-8k``.

.. option:: bssplit=str[,str][,str]

        Sometimes you want even finer grained control of the block sizes
        issued, not just an even split between them.  This option allows you to
        weight various block sizes, so that you are able to define a specific
        amount of block sizes issued. The format for this option is::

                bssplit=blocksize/percentage:blocksize/percentage

        for as many block sizes as needed. So if you want to define a workload
        that has 50% 64k blocks, 10% 4k blocks, and 40% 32k blocks, you would
        write::

                bssplit=4k/10:64k/50:32k/40

        Ordering does not matter. If the percentage is left blank, fio will
        fill in the remaining values evenly. So a bssplit option like this one::

                bssplit=4k/50:1k/:32k/

        would have 50% 4k ios, and 25% 1k and 32k ios. The percentages always
        add up to 100, if bssplit is given a range that adds up to more, it
        will error out.

        Comma-separated values may be specified for reads, writes, and trims as
        described in :option:`blocksize`.

        If you want a workload that has 50% 2k reads and 50% 4k reads, while
        having 90% 4k writes and 10% 8k writes, you would specify::

                bssplit=2k/50:4k/50,4k/90:8k/10

        Fio supports defining up to 64 different weights for each data
        direction.

.. option:: blocksize_unaligned, bs_unaligned

        If set, fio will issue I/O units with any size within
        :option:`blocksize_range`, not just multiples of the minimum size.  This
        typically won't work with direct I/O, as that normally requires sector
        alignment.

.. option:: bs_is_seq_rand=bool

        If this option is set, fio will use the normal read,write blocksize settings
        as sequential,random blocksize settings instead. Any random read or write
        will use the WRITE blocksize settings, and any sequential read or write will
        use the READ blocksize settings.

.. option:: blockalign=int[,int][,int], ba=int[,int][,int]

        Boundary to which fio will align random I/O units.  Default:
        :option:`blocksize`.  Minimum alignment is typically 512b for using direct
        I/O, though it usually depends on the hardware block size. This option is
        mutually exclusive with using a random map for files, so it will turn off
        that option.  Comma-separated values may be specified for reads, writes, and
        trims as described in :option:`blocksize`.


Buffers and memory
~~~~~~~~~~~~~~~~~~

.. option:: zero_buffers

        Initialize buffers with all zeros. Default: fill buffers with random data.

.. option:: refill_buffers

        If this option is given, fio will refill the I/O buffers on every
        submit. Only makes sense if :option:`zero_buffers` isn't specified,
        naturally. Defaults to being unset i.e., the buffer is only filled at
        init time and the data in it is reused when possible but if any of
        :option:`verify`, :option:`buffer_compress_percentage` or
        :option:`dedupe_percentage` are enabled then `refill_buffers` is also
        automatically enabled.

.. option:: scramble_buffers=bool

        If :option:`refill_buffers` is too costly and the target is using data
        deduplication, then setting this option will slightly modify the I/O buffer
        contents to defeat normal de-dupe attempts. This is not enough to defeat
        more clever block compression attempts, but it will stop naive dedupe of
        blocks. Default: true.

.. option:: buffer_compress_percentage=int

        If this is set, then fio will attempt to provide I/O buffer content
        (on WRITEs) that compresses to the specified level. Fio does this by
        providing a mix of random data followed by fixed pattern data. The
        fixed pattern is either zeros, or the pattern specified by
        :option:`buffer_pattern`. If the `buffer_pattern` option is used, it
        might skew the compression ratio slightly. Setting
        `buffer_compress_percentage` to a value other than 100 will also
        enable :option:`refill_buffers` in order to reduce the likelihood that
        adjacent blocks are so similar that they over compress when seen
        together. See :option:`buffer_compress_chunk` for how to set a finer or
        coarser granularity for the random/fixed data region. Defaults to unset
        i.e., buffer data will not adhere to any compression level.

.. option:: buffer_compress_chunk=int

        This setting allows fio to manage how big the random/fixed data region
        is when using :option:`buffer_compress_percentage`. When
        `buffer_compress_chunk` is set to some non-zero value smaller than the
        block size, fio can repeat the random/fixed region throughout the I/O
        buffer at the specified interval (which particularly useful when
        bigger block sizes are used for a job). When set to 0, fio will use a
        chunk size that matches the block size resulting in a single
        random/fixed region within the I/O buffer. Defaults to 512. When the
        unit is omitted, the value is interpreted in bytes.

.. option:: buffer_pattern=str

        If set, fio will fill the I/O buffers with this pattern or with the contents
        of a file. If not set, the contents of I/O buffers are defined by the other
        options related to buffer contents. The setting can be any pattern of bytes,
        and can be prefixed with 0x for hex values. It may also be a string, where
        the string must then be wrapped with ``""``. Or it may also be a filename,
        where the filename must be wrapped with ``''`` in which case the file is
        opened and read. Note that not all the file contents will be read if that
        would cause the buffers to overflow. So, for example::

                buffer_pattern='filename'

        or::

                buffer_pattern="abcd"

        or::

                buffer_pattern=-12

        or::

                buffer_pattern=0xdeadface

        Also you can combine everything together in any order::

                buffer_pattern=0xdeadface"abcd"-12'filename'

.. option:: dedupe_percentage=int

        If set, fio will generate this percentage of identical buffers when
        writing. These buffers will be naturally dedupable. The contents of the
        buffers depend on what other buffer compression settings have been set. It's
        possible to have the individual buffers either fully compressible, or not at
        all -- this option only controls the distribution of unique buffers. Setting
        this option will also enable :option:`refill_buffers` to prevent every buffer
        being identical.

.. option:: dedupe_mode=str

        If ``dedupe_percentage=<int>`` is given, then this option controls how fio
        generates the dedupe buffers.

                **repeat**
                        Generate dedupe buffers by repeating previous writes
                **working_set**
                        Generate dedupe buffers from working set

        ``repeat`` is the default option for fio. Dedupe buffers are generated
        by repeating previous unique write.

        ``working_set`` is a more realistic workload.
        With ``working_set``, ``dedupe_working_set_percentage=<int>`` should be provided.
        Given that, fio will use the initial unique write buffers as its working set.
        Upon deciding to dedupe, fio will randomly choose a buffer from the working set.
        Note that by using ``working_set`` the dedupe percentage will converge
        to the desired over time while ``repeat`` maintains the desired percentage
        throughout the job.

.. option:: dedupe_working_set_percentage=int

        If ``dedupe_mode=<str>`` is set to ``working_set``, then this controls
        the percentage of size of the file or device used as the buffers
        fio will choose to generate the dedupe buffers from

        Note that size needs to be explicitly provided and only 1 file per
        job is supported

.. option:: dedupe_global=bool

        This controls whether the deduplication buffers will be shared amongst
        all jobs that have this option set. The buffers are spread evenly between
        participating jobs.

.. option:: invalidate=bool

        Invalidate the buffer/page cache parts of the files to be used prior to
        starting I/O if the platform and file type support it.  Defaults to true.
        This will be ignored if :option:`pre_read` is also specified for the
        same job.

.. option:: sync=str

        Whether, and what type, of synchronous I/O to use for writes.  The allowed
        values are:

                **none**
                        Do not use synchronous IO, the default.

                **0**
                        Same as **none**.

                **sync**
                        Use synchronous file IO. For the majority of I/O engines,
                        this means using O_SYNC.

                **1**
                        Same as **sync**.

                **dsync**
                        Use synchronous data IO. For the majority of I/O engines,
                        this means using O_DSYNC.


.. option:: iomem=str, mem=str

        Fio can use various types of memory as the I/O unit buffer.  The allowed
        values are:

                **malloc**
                        Use memory from :manpage:`malloc(3)` as the buffers.  Default memory
                        type.

                **shm**
                        Use shared memory as the buffers. Allocated through
                        :manpage:`shmget(2)`.

                **shmhuge**
                        Same as shm, but use huge pages as backing.

                **mmap**
                        Use :manpage:`mmap(2)` to allocate buffers. May either be anonymous memory, or can
                        be file backed if a filename is given after the option. The format
                        is `mem=mmap:/path/to/file`.

                **mmaphuge**
                        Use a memory mapped huge file as the buffer backing. Append filename
                        after mmaphuge, ala `mem=mmaphuge:/hugetlbfs/file`.

                **mmapshared**
                        Same as mmap, but use a MMAP_SHARED mapping.

                **cudamalloc**
                        Use GPU memory as the buffers for GPUDirect RDMA benchmark.
                        The :option:`ioengine` must be `rdma`.

        The area allocated is a function of the maximum allowed bs size for the job,
        multiplied by the I/O depth given. Note that for **shmhuge** and
        **mmaphuge** to work, the system must have free huge pages allocated. This
        can normally be checked and set by reading/writing
        :file:`/proc/sys/vm/nr_hugepages` on a Linux system. Fio assumes a huge page
        is 2 or 4MiB in size depending on the platform. So to calculate the
        number of huge pages you need for a given job file, add up the I/O
        depth of all jobs (normally one unless :option:`iodepth` is used) and
        multiply by the maximum bs set. Then divide that number by the huge
        page size. You can see the size of the huge pages in
        :file:`/proc/meminfo`. If no huge pages are allocated by having a
        non-zero number in `nr_hugepages`, using **mmaphuge** or **shmhuge**
        will fail. Also see :option:`hugepage-size`.

        **mmaphuge** also needs to have hugetlbfs mounted and the file location
        should point there. So if it's mounted in :file:`/huge`, you would use
        `mem=mmaphuge:/huge/somefile`.

.. option:: iomem_align=int, mem_align=int

        This indicates the memory alignment of the I/O memory buffers.  Note that
        the given alignment is applied to the first I/O unit buffer, if using
        :option:`iodepth` the alignment of the following buffers are given by the
        :option:`bs` used. In other words, if using a :option:`bs` that is a
        multiple of the page sized in the system, all buffers will be aligned to
        this value. If using a :option:`bs` that is not page aligned, the alignment
        of subsequent I/O memory buffers is the sum of the :option:`iomem_align` and
        :option:`bs` used.

.. option:: hugepage-size=int

        Defines the size of a huge page. Must at least be equal to the system
        setting, see :file:`/proc/meminfo` and
        :file:`/sys/kernel/mm/hugepages/`. Defaults to 2 or 4MiB depending on
        the platform.  Should probably always be a multiple of megabytes, so
        using ``hugepage-size=Xm`` is the preferred way to set this to avoid
        setting a non-pow-2 bad value.

.. option:: lockmem=int

        Pin the specified amount of memory with :manpage:`mlock(2)`. Can be used to
        simulate a smaller amount of memory.  The amount specified is per worker.


I/O size
~~~~~~~~

.. option:: size=int

        The total size of file I/O for each thread of this job. Fio will run until
        this many bytes has been transferred, unless runtime is altered by other means
        such as (1) :option:`runtime`, (2) :option:`io_size` (3) :option:`number_ios`,
        (4) gaps/holes while doing I/O's such as ``rw=read:16K``, or (5) sequential
        I/O reaching end of the file which is possible when :option:`percentage_random`
        is less than 100.
        Fio will divide this size between the available files determined by options
        such as :option:`nrfiles`, :option:`filename`, unless :option:`filesize` is
        specified by the job. If the result of division happens to be 0, the size is
        set to the physical size of the given files or devices if they exist.
        If this option is not specified, fio will use the full size of the given
        files or devices.  If the files do not exist, size must be given. It is also
        possible to give size as a percentage between 1 and 100. If ``size=20%`` is
        given, fio will use 20% of the full size of the given files or devices.
        In ZBD mode, value can also be set as number of zones using 'z'.
        Can be combined with :option:`offset` to constrain the start and end range
        that I/O will be done within.

.. option:: io_size=int, io_limit=int

        Normally fio operates within the region set by :option:`size`, which means
        that the :option:`size` option sets both the region and size of I/O to be
        performed. Sometimes that is not what you want. With this option, it is
        possible to define just the amount of I/O that fio should do. For instance,
        if :option:`size` is set to 20GiB and :option:`io_size` is set to 5GiB, fio
        will perform I/O within the first 20GiB but exit when 5GiB have been
        done. The opposite is also possible -- if :option:`size` is set to 20GiB,
        and :option:`io_size` is set to 40GiB, then fio will do 40GiB of I/O within
        the 0..20GiB region.

.. option:: filesize=irange(int)

        Individual file sizes. May be a range, in which case fio will select sizes for
        files at random within the given range. If not given, each created file is the
        same size. This option overrides :option:`size` in terms of file size, i.e. if
        :option:`filesize` is specified then :option:`size` becomes merely the default
        for :option:`io_size` and has no effect at all if :option:`io_size` is set
        explicitly.

.. option:: file_append=bool

        Perform I/O after the end of the file. Normally fio will operate within the
        size of a file. If this option is set, then fio will append to the file
        instead. This has identical behavior to setting :option:`offset` to the size
        of a file.  This option is ignored on non-regular files.

.. option:: fill_device=bool, fill_fs=bool

        Sets size to something really large and waits for ENOSPC (no space left on
        device) or EDQUOT (disk quota exceeded)
        as the terminating condition. Only makes sense with sequential
        write. For a read workload, the mount point will be filled first then I/O
        started on the result. This option doesn't make sense if operating on a raw
        device node, since the size of that is already known by the file system.
        Additionally, writing beyond end-of-device will not return ENOSPC there.


I/O engine
~~~~~~~~~~

.. option:: ioengine=str

        Defines how the job issues I/O to the file. The following types are defined:

                **sync**
                        Basic :manpage:`read(2)` or :manpage:`write(2)`
                        I/O. :manpage:`lseek(2)` is used to position the I/O location.
                        See :option:`fsync` and :option:`fdatasync` for syncing write I/Os.

                **psync**
                        Basic :manpage:`pread(2)` or :manpage:`pwrite(2)` I/O.  Default on
                        all supported operating systems except for Windows.

                **vsync**
                        Basic :manpage:`readv(2)` or :manpage:`writev(2)` I/O.  Will emulate
                        queuing by coalescing adjacent I/Os into a single submission.

                **pvsync**
                        Basic :manpage:`preadv(2)` or :manpage:`pwritev(2)` I/O.

                **pvsync2**
                        Basic :manpage:`preadv2(2)` or :manpage:`pwritev2(2)` I/O.

                **io_uring**
                        Fast Linux native asynchronous I/O. Supports async IO
                        for both direct and buffered IO.
                        This engine defines engine specific options.

                **io_uring_cmd**
                        Fast Linux native asynchronous I/O for pass through commands.
                        This engine defines engine specific options.

                **libaio**
                        Linux native asynchronous I/O. Note that Linux may only support
                        queued behavior with non-buffered I/O (set ``direct=1`` or
                        ``buffered=0``).
                        This engine defines engine specific options.

                **posixaio**
                        POSIX asynchronous I/O using :manpage:`aio_read(3)` and
                        :manpage:`aio_write(3)`.

                **solarisaio**
                        Solaris native asynchronous I/O.

                **windowsaio**
                        Windows native asynchronous I/O.  Default on Windows.

                **mmap**
                        File is memory mapped with :manpage:`mmap(2)` and data copied
                        to/from using :manpage:`memcpy(3)`.

                **splice**
                        :manpage:`splice(2)` is used to transfer the data and
                        :manpage:`vmsplice(2)` to transfer data from user space to the
                        kernel.

                **sg**
                        SCSI generic sg v3 I/O. May either be synchronous using the SG_IO
                        ioctl, or if the target is an sg character device we use
                        :manpage:`read(2)` and :manpage:`write(2)` for asynchronous
                        I/O. Requires :option:`filename` option to specify either block or
                        character devices. This engine supports trim operations.
                        The sg engine includes engine specific options.

                **libzbc**
                        Read, write, trim and ZBC/ZAC operations to a zoned
                        block device using libzbc library. The target can be
                        either an SG character device or a block device file.

                **null**
                        Doesn't transfer any data, just pretends to.  This is mainly used to
                        exercise fio itself and for debugging/testing purposes.

                **net**
                        Transfer over the network to given ``host:port``.  Depending on the
                        :option:`protocol` used, the :option:`hostname`, :option:`port`,
                        :option:`listen` and :option:`filename` options are used to specify
                        what sort of connection to make, while the :option:`protocol` option
                        determines which protocol will be used.  This engine defines engine
                        specific options.

                **netsplice**
                        Like **net**, but uses :manpage:`splice(2)` and
                        :manpage:`vmsplice(2)` to map data and send/receive.
                        This engine defines engine specific options.

                **cpuio**
                        Doesn't transfer any data, but burns CPU cycles according to the
                        :option:`cpuload`, :option:`cpuchunks` and :option:`cpumode` options.
                        Setting :option:`cpuload`\=85 will cause that job to do nothing but burn 85%
                        of the CPU. In case of SMP machines, use :option:`numjobs`\=<nr_of_cpu>
                        to get desired CPU usage, as the cpuload only loads a
                        single CPU at the desired rate. A job never finishes unless there is
                        at least one non-cpuio job.
                        Setting :option:`cpumode`\=qsort replace the default noop instructions loop
                        by a qsort algorithm to consume more energy.

                **rdma**
                        The RDMA I/O engine supports both RDMA memory semantics
                        (RDMA_WRITE/RDMA_READ) and channel semantics (Send/Recv) for the
                        InfiniBand, RoCE and iWARP protocols. This engine defines engine
                        specific options.

                **falloc**
                        I/O engine that does regular fallocate to simulate data transfer as
                        fio ioengine.

                        DDIR_READ
                                does fallocate(,mode = FALLOC_FL_KEEP_SIZE,).

                        DDIR_WRITE
                                does fallocate(,mode = 0).

                        DDIR_TRIM
                                does fallocate(,mode = FALLOC_FL_KEEP_SIZE|FALLOC_FL_PUNCH_HOLE).

                **ftruncate**
                        I/O engine that sends :manpage:`ftruncate(2)` operations in response
                        to write (DDIR_WRITE) events. Each ftruncate issued sets the file's
                        size to the current block offset. :option:`blocksize` is ignored.

                **e4defrag**
                        I/O engine that does regular EXT4_IOC_MOVE_EXT ioctls to simulate
                        defragment activity in request to DDIR_WRITE event.

                **rados**
                        I/O engine supporting direct access to Ceph Reliable Autonomic
                        Distributed Object Store (RADOS) via librados. This ioengine
                        defines engine specific options.

                **rbd**
                        I/O engine supporting direct access to Ceph Rados Block Devices
                        (RBD) via librbd without the need to use the kernel rbd driver. This
                        ioengine defines engine specific options.

                **http**
                        I/O engine supporting GET/PUT requests over HTTP(S) with libcurl to
                        a WebDAV or S3 endpoint.  This ioengine defines engine specific options.

                        This engine only supports direct IO of iodepth=1; you need to scale this
                        via numjobs. blocksize defines the size of the objects to be created.

                        TRIM is translated to object deletion.

                **gfapi**
                        Using GlusterFS libgfapi sync interface to direct access to
                        GlusterFS volumes without having to go through FUSE.  This ioengine
                        defines engine specific options.

                **gfapi_async**
                        Using GlusterFS libgfapi async interface to direct access to
                        GlusterFS volumes without having to go through FUSE. This ioengine
                        defines engine specific options.

                **libhdfs**
                        Read and write through Hadoop (HDFS).  The :option:`filename` option
                        is used to specify host,port of the hdfs name-node to connect.  This
                        engine interprets offsets a little differently.  In HDFS, files once
                        created cannot be modified so random writes are not possible. To
                        imitate this the libhdfs engine expects a bunch of small files to be
                        created over HDFS and will randomly pick a file from them
                        based on the offset generated by fio backend (see the example
                        job file to create such files, use ``rw=write`` option). Please
                        note, it may be necessary to set environment variables to work
                        with HDFS/libhdfs properly.  Each job uses its own connection to
                        HDFS.

                **mtd**
                        Read, write and erase an MTD character device (e.g.,
                        :file:`/dev/mtd0`). Discards are treated as erases. Depending on the
                        underlying device type, the I/O may have to go in a certain pattern,
                        e.g., on NAND, writing sequentially to erase blocks and discarding
                        before overwriting. The `trimwrite` mode works well for this
                        constraint.

                **pmemblk**
                        Read and write using filesystem DAX to a file on a filesystem
                        mounted with DAX on a persistent memory device through the PMDK
                        libpmemblk library.

                **dev-dax**
                        Read and write using device DAX to a persistent memory device (e.g.,
                        /dev/dax0.0) through the PMDK libpmem library.

                **external**
                        Prefix to specify loading an external I/O engine object file. Append
                        the engine filename, e.g. ``ioengine=external:/tmp/foo.o`` to load
                        ioengine :file:`foo.o` in :file:`/tmp`. The path can be either
                        absolute or relative. See :file:`engines/skeleton_external.c` for
                        details of writing an external I/O engine.

                **filecreate**
                        Simply create the files and do no I/O to them.  You still need to
                        set  `filesize` so that all the accounting still occurs, but no
                        actual I/O will be done other than creating the file.

                **filestat**
                        Simply do stat() and do no I/O to the file. You need to set 'filesize'
                        and 'nrfiles', so that files will be created.
                        This engine is to measure file lookup and meta data access.

                **filedelete**
                        Simply delete the files by unlink() and do no I/O to them. You need to set 'filesize'
                        and 'nrfiles', so that the files will be created.
                        This engine is to measure file delete.

                **libpmem**
                        Read and write using mmap I/O to a file on a filesystem
                        mounted with DAX on a persistent memory device through the PMDK
                        libpmem library.

                **ime_psync**
                        Synchronous read and write using DDN's Infinite Memory Engine (IME).
                        This engine is very basic and issues calls to IME whenever an IO is
                        queued.

                **ime_psyncv**
                        Synchronous read and write using DDN's Infinite Memory Engine (IME).
                        This engine uses iovecs and will try to stack as much IOs as possible
                        (if the IOs are "contiguous" and the IO depth is not exceeded)
                        before issuing a call to IME.

                **ime_aio**
                        Asynchronous read and write using DDN's Infinite Memory Engine (IME).
                        This engine will try to stack as much IOs as possible by creating
                        requests for IME. FIO will then decide when to commit these requests.

                **libiscsi**
                        Read and write iscsi lun with libiscsi.

                **nbd**
                        Read and write a Network Block Device (NBD).

                **libcufile**
                        I/O engine supporting libcufile synchronous access to nvidia-fs and a
                        GPUDirect Storage-supported filesystem. This engine performs
                        I/O without transferring buffers between user-space and the kernel,
                        unless :option:`verify` is set or :option:`cuda_io` is `posix`.
                        :option:`iomem` must not be `cudamalloc`. This ioengine defines
                        engine specific options.

                **dfs**
                        I/O engine supporting asynchronous read and write operations to the
                        DAOS File System (DFS) via libdfs.

                **nfs**
                        I/O engine supporting asynchronous read and write operations to
                        NFS filesystems from userspace via libnfs. This is useful for
                        achieving higher concurrency and thus throughput than is possible
                        via kernel NFS.

                **exec**
                        Execute 3rd party tools. Could be used to perform monitoring during jobs runtime.

                **xnvme**
                        I/O engine using the xNVMe C API, for NVMe devices. The xnvme engine provides
                        flexibility to access GNU/Linux Kernel NVMe driver via libaio, IOCTLs, io_uring,
                        the SPDK NVMe driver, or your own custom NVMe driver. The xnvme engine includes
                        engine specific options. (See https://xnvme.io).

                **libblkio**
                        Use the libblkio library
                        (https://gitlab.com/libblkio/libblkio). The specific
                        *driver* to use must be set using
                        :option:`libblkio_driver`. If
                        :option:`mem`/:option:`iomem` is not specified, memory
                        allocation is delegated to libblkio (and so is
                        guaranteed to work with the selected *driver*). One
                        libblkio instance is used per process, so all jobs
                        setting option :option:`thread` will share a single
                        instance (with one queue per thread) and must specify
                        compatible options. Note that some drivers don't allow
                        several instances to access the same device or file
                        simultaneously, but allow it for threads.

I/O engine specific parameters
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In addition, there are some parameters which are only valid when a specific
:option:`ioengine` is in use. These are used identically to normal parameters,
with the caveat that when used on the command line, they must come after the
:option:`ioengine` that defines them is selected.

.. option:: cmdprio_percentage=int[,int] : [io_uring] [libaio]

    Set the percentage of I/O that will be issued with the highest priority.
    Default: 0. A single value applies to reads and writes. Comma-separated
    values may be specified for reads and writes. For this option to be
    effective, NCQ priority must be supported and enabled, and the :option:`direct`
    option must be set. fio must also be run as the root user. Unlike
    slat/clat/lat stats, which can be tracked and reported independently, per
    priority stats only track and report a single type of latency. By default,
    completion latency (clat) will be reported, if :option:`lat_percentiles` is
    set, total latency (lat) will be reported.

.. option:: cmdprio_class=int[,int] : [io_uring] [libaio]

        Set the I/O priority class to use for I/Os that must be issued with
        a priority when :option:`cmdprio_percentage` or
        :option:`cmdprio_bssplit` is set. If not specified when
        :option:`cmdprio_percentage` or :option:`cmdprio_bssplit` is set,
        this defaults to the highest priority class. A single value applies
        to reads and writes. Comma-separated values may be specified for
        reads and writes. See :manpage:`ionice(1)`. See also the
        :option:`prioclass` option.

.. option:: cmdprio=int[,int] : [io_uring] [libaio]

        Set the I/O priority value to use for I/Os that must be issued with
        a priority when :option:`cmdprio_percentage` or
        :option:`cmdprio_bssplit` is set. If not specified when
        :option:`cmdprio_percentage` or :option:`cmdprio_bssplit` is set,
        this defaults to 0.
        Linux limits us to a positive value between 0 and 7, with 0 being the
        highest. A single value applies to reads and writes. Comma-separated
        values may be specified for reads and writes. See :manpage:`ionice(1)`.
        Refer to an appropriate manpage for other operating systems since
        meaning of priority may differ. See also the :option:`prio` option.

.. option:: cmdprio_bssplit=str[,str] : [io_uring] [libaio]

        To get a finer control over I/O priority, this option allows
        specifying the percentage of IOs that must have a priority set
        depending on the block size of the IO. This option is useful only
        when used together with the :option:`bssplit` option, that is,
        multiple different block sizes are used for reads and writes.

        The first accepted format for this option is the same as the format of
        the :option:`bssplit` option:

                cmdprio_bssplit=blocksize/percentage:blocksize/percentage

        In this case, each entry will use the priority class and priority
        level defined by the options :option:`cmdprio_class` and
        :option:`cmdprio` respectively.

        The second accepted format for this option is:

                cmdprio_bssplit=blocksize/percentage/class/level:blocksize/percentage/class/level

        In this case, the priority class and priority level is defined inside
        each entry. In comparison with the first accepted format, the second
        accepted format does not restrict all entries to have the same priority
        class and priority level.

        For both formats, only the read and write data directions are supported,
        values for trim IOs are ignored. This option is mutually exclusive with
        the :option:`cmdprio_percentage` option.

.. option:: fixedbufs : [io_uring] [io_uring_cmd]

        If fio is asked to do direct IO, then Linux will map pages for each
        IO call, and release them when IO is done. If this option is set, the
        pages are pre-mapped before IO is started. This eliminates the need to
        map and release for each IO. This is more efficient, and reduces the
        IO latency as well.

.. option:: nonvectored=int : [io_uring] [io_uring_cmd]

        With this option, fio will use non-vectored read/write commands, where
        address must contain the address directly. Default is -1.

.. option:: force_async=int : [io_uring] [io_uring_cmd]

        Normal operation for io_uring is to try and issue an sqe as
        non-blocking first, and if that fails, execute it in an async manner.
        With this option set to N, then every N request fio will ask sqe to
        be issued in an async manner. Default is 0.

.. option:: registerfiles : [io_uring] [io_uring_cmd]

        With this option, fio registers the set of files being used with the
        kernel. This avoids the overhead of managing file counts in the kernel,
        making the submission and completion part more lightweight. Required
        for the below :option:`sqthread_poll` option.

.. option:: sqthread_poll : [io_uring] [io_uring_cmd] [xnvme]

        Normally fio will submit IO by issuing a system call to notify the
        kernel of available items in the SQ ring. If this option is set, the
        act of submitting IO will be done by a polling thread in the kernel.
        This frees up cycles for fio, at the cost of using more CPU in the
        system. As submission is just the time it takes to fill in the sqe
        entries and any syscall required to wake up the idle kernel thread,
        fio will not report submission latencies.

.. option:: sqthread_poll_cpu=int : [io_uring] [io_uring_cmd]

        When :option:`sqthread_poll` is set, this option provides a way to
        define which CPU should be used for the polling thread.

.. option:: cmd_type=str : [io_uring_cmd]

        Specifies the type of uring passthrough command to be used. Supported
        value is nvme. Default is nvme.

.. option:: hipri

   [io_uring] [io_uring_cmd] [xnvme]

        If this option is set, fio will attempt to use polled IO completions.
        Normal IO completions generate interrupts to signal the completion of
        IO, polled completions do not. Hence they are require active reaping
        by the application. The benefits are more efficient IO for high IOPS
        scenarios, and lower latencies for low queue depth IO.

   [libblkio]

        Use poll queues. This is incompatible with
        :option:`libblkio_wait_mode=eventfd <libblkio_wait_mode>` and
        :option:`libblkio_force_enable_completion_eventfd`.

   [pvsync2]

        Set RWF_HIPRI on I/O, indicating to the kernel that it's of higher priority
        than normal.

   [sg]

        If this option is set, fio will attempt to use polled IO completions.
        This will have a similar effect as (io_uring)hipri. Only SCSI READ and
        WRITE commands will have the SGV4_FLAG_HIPRI set (not UNMAP (trim) nor
        VERIFY). Older versions of the Linux sg driver that do not support
        hipri will simply ignore this flag and do normal IO. The Linux SCSI
        Low Level Driver (LLD) that "owns" the device also needs to support
        hipri (also known as iopoll and mq_poll). The MegaRAID driver is an
        example of a SCSI LLD. Default: clear (0) which does normal
        (interrupted based) IO.

.. option:: userspace_reap : [libaio]

        Normally, with the libaio engine in use, fio will use the
        :manpage:`io_getevents(2)` system call to reap newly returned events.  With
        this flag turned on, the AIO ring will be read directly from user-space to
        reap events. The reaping mode is only enabled when polling for a minimum of
        0 events (e.g. when :option:`iodepth_batch_complete` `=0`).

.. option:: hipri_percentage : [pvsync2]

        When hipri is set this determines the probability of a pvsync2 I/O being high
        priority. The default is 100%.

.. option:: nowait=bool : [pvsync2] [libaio] [io_uring] [io_uring_cmd]

        By default if a request cannot be executed immediately (e.g. resource starvation,
        waiting on locks) it is queued and the initiating process will be blocked until
        the required resource becomes free.

        This option sets the RWF_NOWAIT flag (supported from the 4.14 Linux kernel) and
        the call will return instantly with EAGAIN or a partial result rather than waiting.

        It is useful to also use ignore_error=EAGAIN when using this option.

        Note: glibc 2.27, 2.28 have a bug in syscall wrappers preadv2, pwritev2.
        They return EOPNOTSUP instead of EAGAIN.

        For cached I/O, using this option usually means a request operates only with
        cached data. Currently the RWF_NOWAIT flag does not supported for cached write.

        For direct I/O, requests will only succeed if cache invalidation isn't required,
        file blocks are fully allocated and the disk request could be issued immediately.

.. option:: cpuload=int : [cpuio]

        Attempt to use the specified percentage of CPU cycles. This is a mandatory
        option when using cpuio I/O engine.

.. option:: cpuchunks=int : [cpuio]

        Split the load into cycles of the given time. In microseconds.

.. option:: cpumode=str : [cpuio]

        Specify how to stress the CPU. It can take these two values:

        **noop**
                This is the default where the CPU executes noop instructions.
        **qsort**
                Replace the default noop instructions loop with a qsort algorithm to
                consume more energy.

.. option:: exit_on_io_done=bool : [cpuio]

        Detect when I/O threads are done, then exit.

.. option:: namenode=str : [libhdfs]

        The hostname or IP address of a HDFS cluster namenode to contact.

.. option:: port=int

   [libhdfs]

                The listening port of the HFDS cluster namenode.

   [netsplice], [net]

                The TCP or UDP port to bind to or connect to. If this is used with
                :option:`numjobs` to spawn multiple instances of the same job type, then
                this will be the starting port number since fio will use a range of
                ports.

   [rdma], [librpma_*]

                The port to use for RDMA-CM communication. This should be the same value
                on the client and the server side.

.. option:: hostname=str : [netsplice] [net] [rdma]

        The hostname or IP address to use for TCP, UDP or RDMA-CM based I/O.  If the job
        is a TCP listener or UDP reader, the hostname is not used and must be omitted
        unless it is a valid UDP multicast address.

.. option:: serverip=str : [librpma_*]

        The IP address to be used for RDMA-CM based I/O.

.. option:: direct_write_to_pmem=bool : [librpma_*]

        Set to 1 only when Direct Write to PMem from the remote host is possible.
        Otherwise, set to 0.

.. option:: busy_wait_polling=bool : [librpma_*_server]

        Set to 0 to wait for completion instead of busy-wait polling completion.
        Default: 1.

.. option:: interface=str : [netsplice] [net]

        The IP address of the network interface used to send or receive UDP
        multicast.

.. option:: ttl=int : [netsplice] [net]

        Time-to-live value for outgoing UDP multicast packets. Default: 1.

.. option:: nodelay=bool : [netsplice] [net]

        Set TCP_NODELAY on TCP connections.

.. option:: protocol=str, proto=str : [netsplice] [net]

        The network protocol to use. Accepted values are:

        **tcp**
                Transmission control protocol.
        **tcpv6**
                Transmission control protocol V6.
        **udp**
                User datagram protocol.
        **udpv6**
                User datagram protocol V6.
        **unix**
                UNIX domain socket.

        When the protocol is TCP or UDP, the port must also be given, as well as the
        hostname if the job is a TCP listener or UDP reader. For unix sockets, the
        normal :option:`filename` option should be used and the port is invalid.

.. option:: listen : [netsplice] [net]

        For TCP network connections, tell fio to listen for incoming connections
        rather than initiating an outgoing connection. The :option:`hostname` must
        be omitted if this option is used.

.. option:: pingpong : [netsplice] [net]

        Normally a network writer will just continue writing data, and a network
        reader will just consume packages. If ``pingpong=1`` is set, a writer will
        send its normal payload to the reader, then wait for the reader to send the
        same payload back. This allows fio to measure network latencies. The
        submission and completion latencies then measure local time spent sending or
        receiving, and the completion latency measures how long it took for the
        other end to receive and send back.  For UDP multicast traffic
        ``pingpong=1`` should only be set for a single reader when multiple readers
        are listening to the same address.

.. option:: window_size : [netsplice] [net]

        Set the desired socket buffer size for the connection.

.. option:: mss : [netsplice] [net]

        Set the TCP maximum segment size (TCP_MAXSEG).

.. option:: donorname=str : [e4defrag]

        File will be used as a block donor (swap extents between files).

.. option:: inplace=int : [e4defrag]

        Configure donor file blocks allocation strategy:

        **0**
                Default. Preallocate donor's file on init.
        **1**
                Allocate space immediately inside defragment event, and free right
                after event.

.. option:: clustername=str : [rbd,rados]

        Specifies the name of the Ceph cluster.

.. option:: rbdname=str : [rbd]

        Specifies the name of the RBD.

.. option:: clientname=str : [rbd,rados]

        Specifies the username (without the 'client.' prefix) used to access the
        Ceph cluster. If the *clustername* is specified, the *clientname* shall be
        the full *type.id* string. If no type. prefix is given, fio will add
        'client.' by default.

.. option:: conf=str : [rados]

    Specifies the configuration path of ceph cluster, so conf file does not
    have to be /etc/ceph/ceph.conf.

.. option:: busy_poll=bool : [rbd,rados]

        Poll store instead of waiting for completion. Usually this provides better
        throughput at cost of higher(up to 100%) CPU utilization.

.. option:: touch_objects=bool : [rados]

        During initialization, touch (create if do not exist) all objects (files).
        Touching all objects affects ceph caches and likely impacts test results.
        Enabled by default.

.. option:: pool=str :

   [rbd,rados]

        Specifies the name of the Ceph pool containing RBD or RADOS data.

   [dfs]

        Specify the label or UUID of the DAOS pool to connect to.

.. option:: cont=str : [dfs]

        Specify the label or UUID of the DAOS container to open.

.. option:: chunk_size=int

   [dfs]

        Specify a different chunk size (in bytes) for the dfs file.
        Use DAOS container's chunk size by default.

   [libhdfs]

        The size of the chunk to use for each file.

.. option:: object_class=str : [dfs]

        Specify a different object class for the dfs file.
        Use DAOS container's object class by default.

.. option:: skip_bad=bool : [mtd]

        Skip operations against known bad blocks.

.. option:: hdfsdirectory : [libhdfs]

        libhdfs will create chunk in this HDFS directory.

.. option:: verb=str : [rdma]

        The RDMA verb to use on this side of the RDMA ioengine connection. Valid
        values are write, read, send and recv. These correspond to the equivalent
        RDMA verbs (e.g. write = rdma_write etc.). Note that this only needs to be
        specified on the client side of the connection. See the examples folder.

.. option:: bindname=str : [rdma]

        The name to use to bind the local RDMA-CM connection to a local RDMA device.
        This could be a hostname or an IPv4 or IPv6 address. On the server side this
        will be passed into the rdma_bind_addr() function and on the client site it
        will be used in the rdma_resolve_add() function. This can be useful when
        multiple paths exist between the client and the server or in certain loopback
        configurations.

.. option:: stat_type=str : [filestat]

        Specify stat system call type to measure lookup/getattr performance.
        Default is **stat** for :manpage:`stat(2)`.

.. option:: readfua=bool : [sg]

        With readfua option set to 1, read operations include
        the force unit access (fua) flag. Default is 0.

.. option:: writefua=bool : [sg]

        With writefua option set to 1, write operations include
        the force unit access (fua) flag. Default is 0.

.. option:: sg_write_mode=str : [sg]

        Specify the type of write commands to issue. This option can take three values:

        **write**
                This is the default where write opcodes are issued as usual.
        **write_and_verify**
                Issue WRITE AND VERIFY commands. The BYTCHK bit is set to 0. This
                directs the device to carry out a medium verification with no data
                comparison. The writefua option is ignored with this selection.
        **verify**
                This option is deprecated. Use write_and_verify instead.
        **write_same**
                Issue WRITE SAME commands. This transfers a single block to the device
                and writes this same block of data to a contiguous sequence of LBAs
                beginning at the specified offset. fio's block size parameter specifies
                the amount of data written with each command. However, the amount of data
                actually transferred to the device is equal to the device's block
                (sector) size. For a device with 512 byte sectors, blocksize=8k will
                write 16 sectors with each command. fio will still generate 8k of data
                for each command but only the first 512 bytes will be used and
                transferred to the device. The writefua option is ignored with this
                selection.
        **same**
                This option is deprecated. Use write_same instead.
        **write_same_ndob**
                Issue WRITE SAME(16) commands as above but with the No Data Output
                Buffer (NDOB) bit set. No data will be transferred to the device with
                this bit set. Data written will be a pre-determined pattern such as
                all zeroes.
        **write_stream**
                Issue WRITE STREAM(16) commands. Use the **stream_id** option to specify
                the stream identifier.
        **verify_bytchk_00**
                Issue VERIFY commands with BYTCHK set to 00. This directs the
                device to carry out a medium verification with no data comparison.
        **verify_bytchk_01**
                Issue VERIFY commands with BYTCHK set to 01. This directs the device to
                compare the data on the device with the data transferred to the device.
        **verify_bytchk_11**
                Issue VERIFY commands with BYTCHK set to 11. This transfers a
                single block to the device and compares the contents of this block with the
                data on the device beginning at the specified offset. fio's block size
                parameter specifies the total amount of data compared with this command.
                However, only one block (sector) worth of data is transferred to the device.
                This is similar to the WRITE SAME command except that data is compared instead
                of written.

.. option:: stream_id=int : [sg]

        Set the stream identifier for WRITE STREAM commands. If this is set to 0 (which is not
        a valid stream identifier) fio will open a stream and then close it when done. Default
        is 0.

.. option:: http_host=str : [http]

        Hostname to connect to. For S3, this could be the bucket hostname.
        Default is **localhost**

.. option:: http_user=str : [http]

        Username for HTTP authentication.

.. option:: http_pass=str : [http]

        Password for HTTP authentication.

.. option:: https=str : [http]

        Enable HTTPS instead of http. *on* enables HTTPS; *insecure*
        will enable HTTPS, but disable SSL peer verification (use with
        caution!). Default is **off**

.. option:: http_mode=str : [http]

        Which HTTP access mode to use: *webdav*, *swift*, or *s3*.
        Default is **webdav**

.. option:: http_s3_region=str : [http]

        The S3 region/zone string.
        Default is **us-east-1**

.. option:: http_s3_key=str : [http]

        The S3 secret key.

.. option:: http_s3_keyid=str : [http]

        The S3 key/access id.

.. option:: http_s3_sse_customer_key=str : [http]

        The encryption customer key in SSE server side.

.. option:: http_s3_sse_customer_algorithm=str : [http]

        The encryption customer algorithm in SSE server side.
        Default is **AES256**

.. option:: http_s3_storage_class=str : [http]

        Which storage class to access. User-customizable settings.
        Default is **STANDARD**

.. option:: http_swift_auth_token=str : [http]

        The Swift auth token. See the example configuration file on how
        to retrieve this.

.. option:: http_verbose=int : [http]

        Enable verbose requests from libcurl. Useful for debugging. 1
        turns on verbose logging from libcurl, 2 additionally enables
        HTTP IO tracing. Default is **0**

.. option:: uri=str : [nbd]

        Specify the NBD URI of the server to test.  The string
        is a standard NBD URI
        (see https://github.com/NetworkBlockDevice/nbd/tree/master/doc).
        Example URIs: nbd://localhost:10809
        nbd+unix:///?socket=/tmp/socket
        nbds://tlshost/exportname

.. option:: gpu_dev_ids=str : [libcufile]

        Specify the GPU IDs to use with CUDA. This is a colon-separated list of
        int. GPUs are assigned to workers roundrobin. Default is 0.

.. option:: cuda_io=str : [libcufile]

        Specify the type of I/O to use with CUDA. Default is **cufile**.

        **cufile**
                Use libcufile and nvidia-fs. This option performs I/O directly
                between a GPUDirect Storage filesystem and GPU buffers,
                avoiding use of a bounce buffer. If :option:`verify` is set,
                cudaMemcpy is used to copy verificaton data between RAM and GPU.
                Verification data is copied from RAM to GPU before a write
                and from GPU to RAM after a read. :option:`direct` must be 1.
        **posix**
                Use POSIX to perform I/O with a RAM buffer, and use cudaMemcpy
                to transfer data between RAM and the GPUs. Data is copied from
                GPU to RAM before a write and copied from RAM to GPU after a
                read. :option:`verify` does not affect use of cudaMemcpy.

.. option:: nfs_url=str : [nfs]

        URL in libnfs format, eg nfs://<server|ipv4|ipv6>/path[?arg=val[&arg=val]*]
        Refer to the libnfs README for more details.

.. option:: program=str : [exec]

        Specify the program to execute.

.. option:: arguments=str : [exec]

        Specify arguments to pass to program.
        Some special variables can be expanded to pass fio's job details to the program.

        **%r**
                Replaced by the duration of the job in seconds.
        **%n**
                Replaced by the name of the job.

.. option:: grace_time=int : [exec]

        Specify the time between the SIGTERM and SIGKILL signals. Default is 1 second.

.. option:: std_redirect=bool : [exec]

        If set, stdout and stderr streams are redirected to files named from the job name. Default is true.

.. option:: xnvme_async=str : [xnvme]

        Select the xnvme async command interface. This can take these values.

        **emu**
                This is default and use to emulate asynchronous I/O by using a
                single thread to create a queue pair on top of a synchronous
                I/O interface using the NVMe driver IOCTL.
        **thrpool**
                Emulate an asynchronous I/O interface with a pool of userspace
                threads on top of a synchronous I/O interface using the NVMe
                driver IOCTL. By default four threads are used.
        **io_uring**
                Linux native asynchronous I/O interface which supports both
                direct and buffered I/O.
        **io_uring_cmd**
                Fast Linux native asynchronous I/O interface for NVMe pass
                through commands. This only works with NVMe character device
                (/dev/ngXnY).
        **libaio**
                Use Linux aio for Asynchronous I/O.
        **posix**
                Use the posix asynchronous I/O interface to perform one or
                more I/O operations asynchronously.
        **nil**
                Do not transfer any data; just pretend to. This is mainly used
                for introspective performance evaluation.

.. option:: xnvme_sync=str : [xnvme]

        Select the xnvme synchronous command interface. This can take these values.

        **nvme**
                This is default and uses Linux NVMe Driver ioctl() for
                synchronous I/O.
        **psync**
                This supports regular as well as vectored pread() and pwrite()
                commands.
        **block**
                This is the same as psync except that it also supports zone
                management commands using Linux block layer IOCTLs.

.. option:: xnvme_admin=str : [xnvme]

        Select the xnvme admin command interface. This can take these values.

        **nvme**
                This is default and uses linux NVMe Driver ioctl() for admin
                commands.
        **block**
                Use Linux Block Layer ioctl() and sysfs for admin commands.

.. option:: xnvme_dev_nsid=int : [xnvme]

        xnvme namespace identifier for userspace NVMe driver, such as SPDK.

.. option:: xnvme_iovec=int : [xnvme]

        If this option is set. xnvme will use vectored read/write commands.

.. option:: libblkio_driver=str : [libblkio]

        The libblkio *driver* to use. Different drivers access devices through
        different underlying interfaces. Available drivers depend on the
        libblkio version in use and are listed at
        https://libblkio.gitlab.io/libblkio/blkio.html#drivers

.. option:: libblkio_path=str : [libblkio]

        Sets the value of the driver-specific "path" property before connecting
        the libblkio instance, which identifies the target device or file on
        which to perform I/O. Its exact semantics are driver-dependent and not
        all drivers may support it; see
        https://libblkio.gitlab.io/libblkio/blkio.html#drivers

.. option:: libblkio_pre_connect_props=str : [libblkio]

        A colon-separated list of additional libblkio properties to be set after
        creating but before connecting the libblkio instance. Each property must
        have the format ``<name>=<value>``. Colons can be escaped as ``\:``.
        These are set after the engine sets any other properties, so those can
        be overriden. Available properties depend on the libblkio version in use
        and are listed at
        https://libblkio.gitlab.io/libblkio/blkio.html#properties

.. option:: libblkio_num_entries=int : [libblkio]

        Sets the value of the driver-specific "num-entries" property before
        starting the libblkio instance. Its exact semantics are driver-dependent
        and not all drivers may support it; see
        https://libblkio.gitlab.io/libblkio/blkio.html#drivers

.. option:: libblkio_queue_size=int : [libblkio]

        Sets the value of the driver-specific "queue-size" property before
        starting the libblkio instance. Its exact semantics are driver-dependent
        and not all drivers may support it; see
        https://libblkio.gitlab.io/libblkio/blkio.html#drivers

.. option:: libblkio_pre_start_props=str : [libblkio]

        A colon-separated list of additional libblkio properties to be set after
        connecting but before starting the libblkio instance. Each property must
        have the format ``<name>=<value>``. Colons can be escaped as ``\:``.
        These are set after the engine sets any other properties, so those can
        be overriden. Available properties depend on the libblkio version in use
        and are listed at
        https://libblkio.gitlab.io/libblkio/blkio.html#properties

.. option:: libblkio_vectored : [libblkio]

        Submit vectored read and write requests.

.. option:: libblkio_write_zeroes_on_trim : [libblkio]

        Submit trims as "write zeroes" requests instead of discard requests.

.. option:: libblkio_wait_mode=str : [libblkio]

        How to wait for completions:

        **block** (default)
                Use a blocking call to ``blkioq_do_io()``.
        **eventfd**
                Use a blocking call to ``read()`` on the completion eventfd.
        **loop**
                Use a busy loop with a non-blocking call to ``blkioq_do_io()``.

.. option:: libblkio_force_enable_completion_eventfd : [libblkio]

        Enable the queue's completion eventfd even when unused. This may impact
        performance. The default is to enable it only if
        :option:`libblkio_wait_mode=eventfd <libblkio_wait_mode>`.

I/O depth
~~~~~~~~~

.. option:: iodepth=int

        Number of I/O units to keep in flight against the file.  Note that
        increasing *iodepth* beyond 1 will not affect synchronous ioengines (except
        for small degrees when :option:`verify_async` is in use).  Even async
        engines may impose OS restrictions causing the desired depth not to be
        achieved.  This may happen on Linux when using libaio and not setting
        :option:`direct`\=1, since buffered I/O is not async on that OS.  Keep an
        eye on the I/O depth distribution in the fio output to verify that the
        achieved depth is as expected. Default: 1.

.. option:: iodepth_batch_submit=int, iodepth_batch=int

        This defines how many pieces of I/O to submit at once.  It defaults to 1
        which means that we submit each I/O as soon as it is available, but can be
        raised to submit bigger batches of I/O at the time. If it is set to 0 the
        :option:`iodepth` value will be used.

.. option:: iodepth_batch_complete_min=int, iodepth_batch_complete=int

        This defines how many pieces of I/O to retrieve at once. It defaults to 1
        which means that we'll ask for a minimum of 1 I/O in the retrieval process
        from the kernel. The I/O retrieval will go on until we hit the limit set by
        :option:`iodepth_low`. If this variable is set to 0, then fio will always
        check for completed events before queuing more I/O. This helps reduce I/O
        latency, at the cost of more retrieval system calls.

.. option:: iodepth_batch_complete_max=int

        This defines maximum pieces of I/O to retrieve at once. This variable should
        be used along with :option:`iodepth_batch_complete_min`\=int variable,
        specifying the range of min and max amount of I/O which should be
        retrieved. By default it is equal to the :option:`iodepth_batch_complete_min`
        value.

        Example #1::

                iodepth_batch_complete_min=1
                iodepth_batch_complete_max=<iodepth>

        which means that we will retrieve at least 1 I/O and up to the whole
        submitted queue depth. If none of I/O has been completed yet, we will wait.

        Example #2::

                iodepth_batch_complete_min=0
                iodepth_batch_complete_max=<iodepth>

        which means that we can retrieve up to the whole submitted queue depth, but
        if none of I/O has been completed yet, we will NOT wait and immediately exit
        the system call. In this example we simply do polling.

.. option:: iodepth_low=int

        The low water mark indicating when to start filling the queue
        again. Defaults to the same as :option:`iodepth`, meaning that fio will
        attempt to keep the queue full at all times.  If :option:`iodepth` is set to
        e.g. 16 and *iodepth_low* is set to 4, then after fio has filled the queue of
        16 requests, it will let the depth drain down to 4 before starting to fill
        it again.

.. option:: serialize_overlap=bool

        Serialize in-flight I/Os that might otherwise cause or suffer from data races.
        When two or more I/Os are submitted simultaneously, there is no guarantee that
        the I/Os will be processed or completed in the submitted order. Further, if
        two or more of those I/Os are writes, any overlapping region between them can
        become indeterminate/undefined on certain storage. These issues can cause
        verification to fail erratically when at least one of the racing I/Os is
        changing data and the overlapping region has a non-zero size. Setting
        ``serialize_overlap`` tells fio to avoid provoking this behavior by explicitly
        serializing in-flight I/Os that have a non-zero overlap. Note that setting
        this option can reduce both performance and the :option:`iodepth` achieved.

        This option only applies to I/Os issued for a single job except when it is
        enabled along with :option:`io_submit_mode`\=offload. In offload mode, fio
        will check for overlap among all I/Os submitted by offload jobs with :option:`serialize_overlap`
        enabled.

        Default: false.

.. option:: io_submit_mode=str

        This option controls how fio submits the I/O to the I/O engine. The default
        is `inline`, which means that the fio job threads submit and reap I/O
        directly. If set to `offload`, the job threads will offload I/O submission
        to a dedicated pool of I/O threads. This requires some coordination and thus
        has a bit of extra overhead, especially for lower queue depth I/O where it
        can increase latencies. The benefit is that fio can manage submission rates
        independently of the device completion rates. This avoids skewed latency
        reporting if I/O gets backed up on the device side (the coordinated omission
        problem). Note that this option cannot reliably be used with async IO
        engines.


I/O rate
~~~~~~~~

.. option:: thinktime=time

        Stall the job for the specified period of time after an I/O has completed before issuing the
        next. May be used to simulate processing being done by an application.
        When the unit is omitted, the value is interpreted in microseconds.  See
        :option:`thinktime_blocks`, :option:`thinktime_iotime` and :option:`thinktime_spin`.

.. option:: thinktime_spin=time

        Only valid if :option:`thinktime` is set - pretend to spend CPU time doing
        something with the data received, before falling back to sleeping for the
        rest of the period specified by :option:`thinktime`.  When the unit is
        omitted, the value is interpreted in microseconds.

.. option:: thinktime_blocks=int

        Only valid if :option:`thinktime` is set - control how many blocks to issue,
        before waiting :option:`thinktime` usecs. If not set, defaults to 1 which will make
        fio wait :option:`thinktime` usecs after every block. This effectively makes any
        queue depth setting redundant, since no more than 1 I/O will be queued
        before we have to complete it and do our :option:`thinktime`. In other words, this
        setting effectively caps the queue depth if the latter is larger.

.. option:: thinktime_blocks_type=str

        Only valid if :option:`thinktime` is set - control how :option:`thinktime_blocks`
        triggers. The default is `complete`, which triggers thinktime when fio completes
        :option:`thinktime_blocks` blocks. If this is set to `issue`, then the trigger happens
        at the issue side.

.. option:: thinktime_iotime=time

        Only valid if :option:`thinktime` is set - control :option:`thinktime`
        interval by time. The :option:`thinktime` stall is repeated after IOs
        are executed for :option:`thinktime_iotime`. For example,
        ``--thinktime_iotime=9s --thinktime=1s`` repeat 10-second cycle with IOs
        for 9 seconds and stall for 1 second. When the unit is omitted,
        :option:`thinktime_iotime` is interpreted as a number of seconds. If
        this option is used together with :option:`thinktime_blocks`, the
        :option:`thinktime` stall is repeated after :option:`thinktime_iotime`
        or after :option:`thinktime_blocks` IOs, whichever happens first.

.. option:: rate=int[,int][,int]

        Cap the bandwidth used by this job. The number is in bytes/sec, the normal
        suffix rules apply.  Comma-separated values may be specified for reads,
        writes, and trims as described in :option:`blocksize`.

        For example, using `rate=1m,500k` would limit reads to 1MiB/sec and writes to
        500KiB/sec.  Capping only reads or writes can be done with `rate=,500k` or
        `rate=500k,` where the former will only limit writes (to 500KiB/sec) and the
        latter will only limit reads.

.. option:: rate_min=int[,int][,int]

        Tell fio to do whatever it can to maintain at least this bandwidth. Failing
        to meet this requirement will cause the job to exit.  Comma-separated values
        may be specified for reads, writes, and trims as described in
        :option:`blocksize`.

.. option:: rate_iops=int[,int][,int]

        Cap the bandwidth to this number of IOPS. Basically the same as
        :option:`rate`, just specified independently of bandwidth. If the job is
        given a block size range instead of a fixed value, the smallest block size
        is used as the metric.  Comma-separated values may be specified for reads,
        writes, and trims as described in :option:`blocksize`.

.. option:: rate_iops_min=int[,int][,int]

        If fio doesn't meet this rate of I/O, it will cause the job to exit.
        Comma-separated values may be specified for reads, writes, and trims as
        described in :option:`blocksize`.

.. option:: rate_process=str

        This option controls how fio manages rated I/O submissions. The default is
        `linear`, which submits I/O in a linear fashion with fixed delays between
        I/Os that gets adjusted based on I/O completion rates. If this is set to
        `poisson`, fio will submit I/O based on a more real world random request
        flow, known as the Poisson process
        (https://en.wikipedia.org/wiki/Poisson_point_process). The lambda will be
        10^6 / IOPS for the given workload.

.. option:: rate_ignore_thinktime=bool

        By default, fio will attempt to catch up to the specified rate setting,
        if any kind of thinktime setting was used. If this option is set, then
        fio will ignore the thinktime and continue doing IO at the specified
        rate, instead of entering a catch-up mode after thinktime is done.


I/O latency
~~~~~~~~~~~

.. option:: latency_target=time

        If set, fio will attempt to find the max performance point that the given
        workload will run at while maintaining a latency below this target.  When
        the unit is omitted, the value is interpreted in microseconds.  See
        :option:`latency_window` and :option:`latency_percentile`.

.. option:: latency_window=time

        Used with :option:`latency_target` to specify the sample window that the job
        is run at varying queue depths to test the performance.  When the unit is
        omitted, the value is interpreted in microseconds.

.. option:: latency_percentile=float

        The percentage of I/Os that must fall within the criteria specified by
        :option:`latency_target` and :option:`latency_window`. If not set, this
        defaults to 100.0, meaning that all I/Os must be equal or below to the value
        set by :option:`latency_target`.

.. option:: latency_run=bool

        Used with :option:`latency_target`. If false (default), fio will find
        the highest queue depth that meets :option:`latency_target` and exit. If
        true, fio will continue running and try to meet :option:`latency_target`
        by adjusting queue depth.

.. option:: max_latency=time[,time][,time]

        If set, fio will exit the job with an ETIMEDOUT error if it exceeds this
        maximum latency. When the unit is omitted, the value is interpreted in
        microseconds. Comma-separated values may be specified for reads, writes,
        and trims as described in :option:`blocksize`.

.. option:: rate_cycle=int

        Average bandwidth for :option:`rate` and :option:`rate_min` over this number
        of milliseconds. Defaults to 1000.


I/O replay
~~~~~~~~~~

.. option:: write_iolog=str

        Write the issued I/O patterns to the specified file. See
        :option:`read_iolog`.  Specify a separate file for each job, otherwise the
        iologs will be interspersed and the file may be corrupt. This file will
        be opened in append mode.

.. option:: read_iolog=str

        Open an iolog with the specified filename and replay the I/O patterns it
        contains. This can be used to store a workload and replay it sometime
        later. The iolog given may also be a blktrace binary file, which allows fio
        to replay a workload captured by :command:`blktrace`. See
        :manpage:`blktrace(8)` for how to capture such logging data. For blktrace
        replay, the file needs to be turned into a blkparse binary data file first
        (``blkparse <device> -o /dev/null -d file_for_fio.bin``).
        You can specify a number of files by separating the names with a ':'
        character. See the :option:`filename` option for information on how to
        escape ':' characters within the file names. These files will
        be sequentially assigned to job clones created by :option:`numjobs`.
        '-' is a reserved name, meaning read from stdin, notably if
        :option:`filename` is set to '-' which means stdin as well, then
        this flag can't be set to '-'.

.. option:: read_iolog_chunked=bool

        Determines how iolog is read. If false(default) entire :option:`read_iolog`
        will be read at once. If selected true, input from iolog will be read
        gradually. Useful when iolog is very large, or it is generated.

.. option:: merge_blktrace_file=str

        When specified, rather than replaying the logs passed to :option:`read_iolog`,
        the logs go through a merge phase which aggregates them into a single
        blktrace. The resulting file is then passed on as the :option:`read_iolog`
        parameter. The intention here is to make the order of events consistent.
        This limits the influence of the scheduler compared to replaying multiple
        blktraces via concurrent jobs.

.. option:: merge_blktrace_scalars=float_list

        This is a percentage based option that is index paired with the list of
        files passed to :option:`read_iolog`. When merging is performed, scale
        the time of each event by the corresponding amount. For example,
        ``--merge_blktrace_scalars="50:100"`` runs the first trace in halftime
        and the second trace in realtime. This knob is separately tunable from
        :option:`replay_time_scale` which scales the trace during runtime and
        does not change the output of the merge unlike this option.

.. option:: merge_blktrace_iters=float_list

        This is a whole number option that is index paired with the list of files
        passed to :option:`read_iolog`. When merging is performed, run each trace
        for the specified number of iterations. For example,
        ``--merge_blktrace_iters="2:1"`` runs the first trace for two iterations
        and the second trace for one iteration.

.. option:: replay_no_stall=bool

        When replaying I/O with :option:`read_iolog` the default behavior is to
        attempt to respect the timestamps within the log and replay them with the
        appropriate delay between IOPS. By setting this variable fio will not
        respect the timestamps and attempt to replay them as fast as possible while
        still respecting ordering. The result is the same I/O pattern to a given
        device, but different timings.

.. option:: replay_time_scale=int

        When replaying I/O with :option:`read_iolog`, fio will honor the
        original timing in the trace. With this option, it's possible to scale
        the time. It's a percentage option, if set to 50 it means run at 50%
        the original IO rate in the trace. If set to 200, run at twice the
        original IO rate. Defaults to 100.

.. option:: replay_redirect=str

        While replaying I/O patterns using :option:`read_iolog` the default behavior
        is to replay the IOPS onto the major/minor device that each IOP was recorded
        from.  This is sometimes undesirable because on a different machine those
        major/minor numbers can map to a different device.  Changing hardware on the
        same system can also result in a different major/minor mapping.
        ``replay_redirect`` causes all I/Os to be replayed onto the single specified
        device regardless of the device it was recorded
        from. i.e. :option:`replay_redirect`\= :file:`/dev/sdc` would cause all I/O
        in the blktrace or iolog to be replayed onto :file:`/dev/sdc`.  This means
        multiple devices will be replayed onto a single device, if the trace
        contains multiple devices. If you want multiple devices to be replayed
        concurrently to multiple redirected devices you must blkparse your trace
        into separate traces and replay them with independent fio invocations.
        Unfortunately this also breaks the strict time ordering between multiple
        device accesses.

.. option:: replay_align=int

        Force alignment of the byte offsets in a trace to this value. The value
        must be a power of 2.

.. option:: replay_scale=int

        Scale byte offsets down by this factor when replaying traces. Should most
        likely use :option:`replay_align` as well.

.. option:: replay_skip=str

        Sometimes it's useful to skip certain IO types in a replay trace.
        This could be, for instance, eliminating the writes in the trace.
        Or not replaying the trims/discards, if you are redirecting to
        a device that doesn't support them. This option takes a comma
        separated list of read, write, trim, sync.


Threads, processes and job synchronization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. option:: thread

        Fio defaults to creating jobs by using fork, however if this option is
        given, fio will create jobs by using POSIX Threads' function
        :manpage:`pthread_create(3)` to create threads instead.

.. option:: wait_for=str

        If set, the current job won't be started until all workers of the specified
        waitee job are done.

        ``wait_for`` operates on the job name basis, so there are a few
        limitations. First, the waitee must be defined prior to the waiter job
        (meaning no forward references). Second, if a job is being referenced as a
        waitee, it must have a unique name (no duplicate waitees).

.. option:: nice=int

        Run the job with the given nice value. See man :manpage:`nice(2)`.

        On Windows, values less than -15 set the process class to "High"; -1 through
        -15 set "Above Normal"; 1 through 15 "Below Normal"; and above 15 "Idle"
        priority class.

.. option:: prio=int

        Set the I/O priority value of this job. Linux limits us to a positive value
        between 0 and 7, with 0 being the highest.  See man
        :manpage:`ionice(1)`. Refer to an appropriate manpage for other operating
        systems since meaning of priority may differ. For per-command priority
        setting, see I/O engine specific :option:`cmdprio_percentage` and
        :option:`cmdprio` options.

.. option:: prioclass=int

        Set the I/O priority class. See man :manpage:`ionice(1)`. For per-command
        priority setting, see I/O engine specific :option:`cmdprio_percentage`
        and :option:`cmdprio_class` options.

.. option:: cpus_allowed=str

        Controls the same options as :option:`cpumask`, but accepts a textual
        specification of the permitted CPUs instead and CPUs are indexed from 0. So
        to use CPUs 0 and 5 you would specify ``cpus_allowed=0,5``. This option also
        allows a range of CPUs to be specified -- say you wanted a binding to CPUs
        0, 5, and 8 to 15, you would set ``cpus_allowed=0,5,8-15``.

        On Windows, when ``cpus_allowed`` is unset only CPUs from fio's current
        processor group will be used and affinity settings are inherited from the
        system. An fio build configured to target Windows 7 makes options that set
        CPUs processor group aware and values will set both the processor group
        and a CPU from within that group. For example, on a system where processor
        group 0 has 40 CPUs and processor group 1 has 32 CPUs, ``cpus_allowed``
        values between 0 and 39 will bind CPUs from processor group 0 and
        ``cpus_allowed`` values between 40 and 71 will bind CPUs from processor
        group 1. When using ``cpus_allowed_policy=shared`` all CPUs specified by a
        single ``cpus_allowed`` option must be from the same processor group. For
        Windows fio builds not built for Windows 7, CPUs will only be selected from
        (and be relative to) whatever processor group fio happens to be running in
        and CPUs from other processor groups cannot be used.

.. option:: cpus_allowed_policy=str

        Set the policy of how fio distributes the CPUs specified by
        :option:`cpus_allowed` or :option:`cpumask`. Two policies are supported:

                **shared**
                        All jobs will share the CPU set specified.
                **split**
                        Each job will get a unique CPU from the CPU set.

        **shared** is the default behavior, if the option isn't specified. If
        **split** is specified, then fio will assign one cpu per job. If not
        enough CPUs are given for the jobs listed, then fio will roundrobin the CPUs
        in the set.

.. option:: cpumask=int

        Set the CPU affinity of this job. The parameter given is a bit mask of
        allowed CPUs the job may run on. So if you want the allowed CPUs to be 1
        and 5, you would pass the decimal value of (1 << 1 | 1 << 5), or 34. See man
        :manpage:`sched_setaffinity(2)`. This may not work on all supported
        operating systems or kernel versions. This option doesn't work well for a
        higher CPU count than what you can store in an integer mask, so it can only
        control cpus 1-32. For boxes with larger CPU counts, use
        :option:`cpus_allowed`.

.. option:: numa_cpu_nodes=str

        Set this job running on specified NUMA nodes' CPUs. The arguments allow
        comma delimited list of cpu numbers, A-B ranges, or `all`. Note, to enable
        NUMA options support, fio must be built on a system with libnuma-dev(el)
        installed.

.. option:: numa_mem_policy=str

        Set this job's memory policy and corresponding NUMA nodes. Format of the
        arguments::

                <mode>[:<nodelist>]

        ``mode`` is one of the following memory policies: ``default``, ``prefer``,
        ``bind``, ``interleave`` or ``local``. For ``default`` and ``local`` memory
        policies, no node needs to be specified.  For ``prefer``, only one node is
        allowed.  For ``bind`` and ``interleave`` the ``nodelist`` may be as
        follows: a comma delimited list of numbers, A-B ranges, or `all`.

.. option:: cgroup=str

        Add job to this control group. If it doesn't exist, it will be created. The
        system must have a mounted cgroup blkio mount point for this to work. If
        your system doesn't have it mounted, you can do so with::

                # mount -t cgroup -o blkio none /cgroup

.. option:: cgroup_weight=int

        Set the weight of the cgroup to this value. See the documentation that comes
        with the kernel, allowed values are in the range of 100..1000.

.. option:: cgroup_nodelete=bool

        Normally fio will delete the cgroups it has created after the job
        completion. To override this behavior and to leave cgroups around after the
        job completion, set ``cgroup_nodelete=1``.  This can be useful if one wants
        to inspect various cgroup files after job completion. Default: false.

.. option:: flow_id=int

        The ID of the flow. If not specified, it defaults to being a global
        flow. See :option:`flow`.

.. option:: flow=int

        Weight in token-based flow control. If this value is used, then fio
        regulates the activity between two or more jobs sharing the same
        flow_id. Fio attempts to keep each job activity proportional to other
        jobs' activities in the same flow_id group, with respect to requested
        weight per job. That is, if one job has `flow=3', another job has
        `flow=2' and another with `flow=1`, then there will be a roughly 3:2:1
        ratio in how much one runs vs the others.

.. option:: flow_sleep=int

        The period of time, in microseconds, to wait after the flow counter
        has exceeded its proportion before retrying operations.

.. option:: stonewall, wait_for_previous

        Wait for preceding jobs in the job file to exit, before starting this
        one. Can be used to insert serialization points in the job file. A stone
        wall also implies starting a new reporting group, see
        :option:`group_reporting`.

.. option:: exitall

        By default, fio will continue running all other jobs when one job finishes.
        Sometimes this is not the desired action.  Setting ``exitall`` will instead
        make fio terminate all jobs in the same group, as soon as one job of that
        group finishes.

.. option:: exit_what=str

        By default, fio will continue running all other jobs when one job finishes.
        Sometimes this is not the desired action. Setting ``exitall`` will
        instead make fio terminate all jobs in the same group. The option
        ``exit_what`` allows to control which jobs get terminated when ``exitall`` is
        enabled. The default is ``group`` and does not change the behaviour of
        ``exitall``. The setting ``all`` terminates all jobs. The setting ``stonewall``
        terminates all currently running jobs across all groups and continues execution
        with the next stonewalled group.

.. option:: exec_prerun=str

        Before running this job, issue the command specified through
        :manpage:`system(3)`. Output is redirected in a file called
        :file:`jobname.prerun.txt`.

.. option:: exec_postrun=str

        After the job completes, issue the command specified though
        :manpage:`system(3)`. Output is redirected in a file called
        :file:`jobname.postrun.txt`.

.. option:: uid=int

        Instead of running as the invoking user, set the user ID to this value
        before the thread/process does any work.

.. option:: gid=int

        Set group ID, see :option:`uid`.


Verification
~~~~~~~~~~~~

.. option:: verify_only

        Do not perform specified workload, only verify data still matches previous
        invocation of this workload. This option allows one to check data multiple
        times at a later date without overwriting it. This option makes sense only
        for workloads that write data, and does not support workloads with the
        :option:`time_based` option set.

.. option:: do_verify=bool

        Run the verify phase after a write phase. Only valid if :option:`verify` is
        set. Default: true.

.. option:: verify=str

        If writing to a file, fio can verify the file contents after each iteration
        of the job. Each verification method also implies verification of special
        header, which is written to the beginning of each block. This header also
        includes meta information, like offset of the block, block number, timestamp
        when block was written, etc.  :option:`verify` can be combined with
        :option:`verify_pattern` option.  The allowed values are:

                **md5**
                        Use an md5 sum of the data area and store it in the header of
                        each block.

                **crc64**
                        Use an experimental crc64 sum of the data area and store it in the
                        header of each block.

                **crc32c**
                        Use a crc32c sum of the data area and store it in the header of
                        each block. This will automatically use hardware acceleration
                        (e.g. SSE4.2 on an x86 or CRC crypto extensions on ARM64) but will
                        fall back to software crc32c if none is found. Generally the
                        fastest checksum fio supports when hardware accelerated.

                **crc32c-intel**
                        Synonym for crc32c.

                **crc32**
                        Use a crc32 sum of the data area and store it in the header of each
                        block.

                **crc16**
                        Use a crc16 sum of the data area and store it in the header of each
                        block.

                **crc7**
                        Use a crc7 sum of the data area and store it in the header of each
                        block.

                **xxhash**
                        Use xxhash as the checksum function. Generally the fastest software
                        checksum that fio supports.

                **sha512**
                        Use sha512 as the checksum function.

                **sha256**
                        Use sha256 as the checksum function.

                **sha1**
                        Use optimized sha1 as the checksum function.

                **sha3-224**
                        Use optimized sha3-224 as the checksum function.

                **sha3-256**
                        Use optimized sha3-256 as the checksum function.

                **sha3-384**
                        Use optimized sha3-384 as the checksum function.

                **sha3-512**
                        Use optimized sha3-512 as the checksum function.

                **meta**
                        This option is deprecated, since now meta information is included in
                        generic verification header and meta verification happens by
                        default. For detailed information see the description of the
                        :option:`verify` setting. This option is kept because of
                        compatibility's sake with old configurations. Do not use it.

                **pattern**
                        Verify a strict pattern. Normally fio includes a header with some
                        basic information and checksumming, but if this option is set, only
                        the specific pattern set with :option:`verify_pattern` is verified.

                **null**
                        Only pretend to verify. Useful for testing internals with
                        :option:`ioengine`\=null, not for much else.

        This option can be used for repeated burn-in tests of a system to make sure
        that the written data is also correctly read back. If the data direction
        given is a read or random read, fio will assume that it should verify a
        previously written file. If the data direction includes any form of write,
        the verify will be of the newly written data.

        To avoid false verification errors, do not use the norandommap option when
        verifying data with async I/O engines and I/O depths > 1.  Or use the
        norandommap and the lfsr random generator together to avoid writing to the
        same offset with multiple outstanding I/Os.

.. option:: verify_offset=int

        Swap the verification header with data somewhere else in the block before
        writing. It is swapped back before verifying.

.. option:: verify_interval=int

        Write the verification header at a finer granularity than the
        :option:`blocksize`. It will be written for chunks the size of
        ``verify_interval``. :option:`blocksize` should divide this evenly.

.. option:: verify_pattern=str

        If set, fio will fill the I/O buffers with this pattern. Fio defaults to
        filling with totally random bytes, but sometimes it's interesting to fill
        with a known pattern for I/O verification purposes. Depending on the width
        of the pattern, fio will fill 1/2/3/4 bytes of the buffer at the time (it can
        be either a decimal or a hex number).  The ``verify_pattern`` if larger than
        a 32-bit quantity has to be a hex number that starts with either "0x" or
        "0X". Use with :option:`verify`. Also, ``verify_pattern`` supports %o
        format, which means that for each block offset will be written and then
        verified back, e.g.::

                verify_pattern=%o

        Or use combination of everything::

                verify_pattern=0xff%o"abcd"-12

.. option:: verify_fatal=bool

        Normally fio will keep checking the entire contents before quitting on a
        block verification failure. If this option is set, fio will exit the job on
        the first observed failure. Default: false.

.. option:: verify_dump=bool

        If set, dump the contents of both the original data block and the data block
        we read off disk to files. This allows later analysis to inspect just what
        kind of data corruption occurred. Off by default.

.. option:: verify_async=int

        Fio will normally verify I/O inline from the submitting thread. This option
        takes an integer describing how many async offload threads to create for I/O
        verification instead, causing fio to offload the duty of verifying I/O
        contents to one or more separate threads. If using this offload option, even
        sync I/O engines can benefit from using an :option:`iodepth` setting higher
        than 1, as it allows them to have I/O in flight while verifies are running.
        Defaults to 0 async threads, i.e. verification is not asynchronous.

.. option:: verify_async_cpus=str

        Tell fio to set the given CPU affinity on the async I/O verification
        threads. See :option:`cpus_allowed` for the format used.

.. option:: verify_backlog=int

        Fio will normally verify the written contents of a job that utilizes verify
        once that job has completed. In other words, everything is written then
        everything is read back and verified. You may want to verify continually
        instead for a variety of reasons. Fio stores the meta data associated with
        an I/O block in memory, so for large verify workloads, quite a bit of memory
        would be used up holding this meta data. If this option is enabled, fio will
        write only N blocks before verifying these blocks.

.. option:: verify_backlog_batch=int

        Control how many blocks fio will verify if :option:`verify_backlog` is
        set. If not set, will default to the value of :option:`verify_backlog`
        (meaning the entire queue is read back and verified).  If
        ``verify_backlog_batch`` is less than :option:`verify_backlog` then not all
        blocks will be verified, if ``verify_backlog_batch`` is larger than
        :option:`verify_backlog`, some blocks will be verified more than once.

.. option:: verify_state_save=bool

        When a job exits during the write phase of a verify workload, save its
        current state. This allows fio to replay up until that point, if the verify
        state is loaded for the verify read phase. The format of the filename is,
        roughly::

                <type>-<jobname>-<jobindex>-verify.state.

        <type> is "local" for a local run, "sock" for a client/server socket
        connection, and "ip" (192.168.0.1, for instance) for a networked
        client/server connection. Defaults to true.

.. option:: verify_state_load=bool

        If a verify termination trigger was used, fio stores the current write state
        of each thread. This can be used at verification time so that fio knows how
        far it should verify.  Without this information, fio will run a full
        verification pass, according to the settings in the job file used.  Default
        false.

.. option:: trim_percentage=int

        Number of verify blocks to discard/trim.

.. option:: trim_verify_zero=bool

        Verify that trim/discarded blocks are returned as zeros.

.. option:: trim_backlog=int

        Trim after this number of blocks are written.

.. option:: trim_backlog_batch=int

        Trim this number of I/O blocks.

.. option:: experimental_verify=bool

        Enable experimental verification. Standard verify records I/O metadata
        for later use during the verification phase. Experimental verify
        instead resets the file after the write phase and then replays I/Os for
        the verification phase.

Steady state
~~~~~~~~~~~~

.. option:: steadystate=str:float, ss=str:float

        Define the criterion and limit for assessing steady state performance. The
        first parameter designates the criterion whereas the second parameter sets
        the threshold. When the criterion falls below the threshold for the
        specified duration, the job will stop. For example, `iops_slope:0.1%` will
        direct fio to terminate the job when the least squares regression slope
        falls below 0.1% of the mean IOPS. If :option:`group_reporting` is enabled
        this will apply to all jobs in the group. Below is the list of available
        steady state assessment criteria. All assessments are carried out using only
        data from the rolling collection window. Threshold limits can be expressed
        as a fixed value or as a percentage of the mean in the collection window.

        When using this feature, most jobs should include the :option:`time_based`
        and :option:`runtime` options or the :option:`loops` option so that fio does not
        stop running after it has covered the full size of the specified file(s) or device(s).

                **iops**
                        Collect IOPS data. Stop the job if all individual IOPS measurements
                        are within the specified limit of the mean IOPS (e.g., ``iops:2``
                        means that all individual IOPS values must be within 2 of the mean,
                        whereas ``iops:0.2%`` means that all individual IOPS values must be
                        within 0.2% of the mean IOPS to terminate the job).

                **iops_slope**
                        Collect IOPS data and calculate the least squares regression
                        slope. Stop the job if the slope falls below the specified limit.

                **bw**
                        Collect bandwidth data. Stop the job if all individual bandwidth
                        measurements are within the specified limit of the mean bandwidth.

                **bw_slope**
                        Collect bandwidth data and calculate the least squares regression
                        slope. Stop the job if the slope falls below the specified limit.

.. option:: steadystate_duration=time, ss_dur=time

        A rolling window of this duration will be used to judge whether steady state
        has been reached. Data will be collected once per second. The default is 0
        which disables steady state detection.  When the unit is omitted, the
        value is interpreted in seconds.

.. option:: steadystate_ramp_time=time, ss_ramp=time

        Allow the job to run for the specified duration before beginning data
        collection for checking the steady state job termination criterion. The
        default is 0.  When the unit is omitted, the value is interpreted in seconds.


Measurements and reporting
~~~~~~~~~~~~~~~~~~~~~~~~~~

.. option:: per_job_logs=bool

        If set, this generates bw/clat/iops log with per file private filenames. If
        not set, jobs with identical names will share the log filename. Default:
        true.

.. option:: group_reporting

        It may sometimes be interesting to display statistics for groups of jobs as
        a whole instead of for each individual job.  This is especially true if
        :option:`numjobs` is used; looking at individual thread/process output
        quickly becomes unwieldy.  To see the final report per-group instead of
        per-job, use :option:`group_reporting`. Jobs in a file will be part of the
        same reporting group, unless if separated by a :option:`stonewall`, or by
        using :option:`new_group`.

.. option:: new_group

        Start a new reporting group. See: :option:`group_reporting`.  If not given,
        all jobs in a file will be part of the same reporting group, unless
        separated by a :option:`stonewall`.

.. option:: stats=bool

        By default, fio collects and shows final output results for all jobs
        that run. If this option is set to 0, then fio will ignore it in
        the final stat output.

.. option:: write_bw_log=str

        If given, write a bandwidth log for this job. Can be used to store data of
        the bandwidth of the jobs in their lifetime.

        If no str argument is given, the default filename of
        :file:`jobname_type.x.log` is used. Even when the argument is given, fio
        will still append the type of log. So if one specifies::

                write_bw_log=foo

        The actual log name will be :file:`foo_bw.x.log` where `x` is the index
        of the job (`1..N`, where `N` is the number of jobs). If
        :option:`per_job_logs` is false, then the filename will not include the
        `.x` job index.

        The included :command:`fio_generate_plots` script uses :command:`gnuplot` to turn these
        text files into nice graphs. See `Log File Formats`_ for how data is
        structured within the file.

.. option:: write_lat_log=str

        Same as :option:`write_bw_log`, except this option creates I/O
        submission (e.g., :file:`name_slat.x.log`), completion (e.g.,
        :file:`name_clat.x.log`), and total (e.g., :file:`name_lat.x.log`)
        latency files instead. See :option:`write_bw_log` for details about
        the filename format and `Log File Formats`_ for how data is structured
        within the files.

.. option:: write_hist_log=str

        Same as :option:`write_bw_log` but writes an I/O completion latency
        histogram file (e.g., :file:`name_hist.x.log`) instead. Note that this
        file will be empty unless :option:`log_hist_msec` has also been set.
        See :option:`write_bw_log` for details about the filename format and
        `Log File Formats`_ for how data is structured within the file.

.. option:: write_iops_log=str

        Same as :option:`write_bw_log`, but writes an IOPS file (e.g.
        :file:`name_iops.x.log`) instead. Because fio defaults to individual
        I/O logging, the value entry in the IOPS log will be 1 unless windowed
        logging (see :option:`log_avg_msec`) has been enabled. See
        :option:`write_bw_log` for details about the filename format and `Log
        File Formats`_ for how data is structured within the file.

.. option:: log_entries=int

        By default, fio will log an entry in the iops, latency, or bw log for
        every I/O that completes. The initial number of I/O log entries is 1024.
        When the log entries are all used, new log entries are dynamically
        allocated.  This dynamic log entry allocation may negatively impact
        time-related statistics such as I/O tail latencies (e.g. 99.9th percentile
        completion latency). This option allows specifying a larger initial
        number of log entries to avoid run-time allocations of new log entries,
        resulting in more precise time-related I/O statistics.
        Also see :option:`log_avg_msec`. Defaults to 1024.

.. option:: log_avg_msec=int

        By default, fio will log an entry in the iops, latency, or bw log for every
        I/O that completes. When writing to the disk log, that can quickly grow to a
        very large size. Setting this option makes fio average the each log entry
        over the specified period of time, reducing the resolution of the log.  See
        :option:`log_max_value` as well. Defaults to 0, logging all entries.
        Also see `Log File Formats`_.

.. option:: log_hist_msec=int

        Same as :option:`log_avg_msec`, but logs entries for completion latency
        histograms. Computing latency percentiles from averages of intervals using
        :option:`log_avg_msec` is inaccurate. Setting this option makes fio log
        histogram entries over the specified period of time, reducing log sizes for
        high IOPS devices while retaining percentile accuracy.  See
        :option:`log_hist_coarseness` and :option:`write_hist_log` as well.
        Defaults to 0, meaning histogram logging is disabled.

.. option:: log_hist_coarseness=int

        Integer ranging from 0 to 6, defining the coarseness of the resolution of
        the histogram logs enabled with :option:`log_hist_msec`. For each increment
        in coarseness, fio outputs half as many bins. Defaults to 0, for which
        histogram logs contain 1216 latency bins. See :option:`write_hist_log`
        and `Log File Formats`_.

.. option:: log_max_value=bool

        If :option:`log_avg_msec` is set, fio logs the average over that window. If
        you instead want to log the maximum value, set this option to 1. Defaults to
        0, meaning that averaged values are logged.

.. option:: log_offset=bool

        If this is set, the iolog options will include the byte offset for the I/O
        entry as well as the other data values. Defaults to 0 meaning that
        offsets are not present in logs. Also see `Log File Formats`_.

.. option:: log_compression=int

        If this is set, fio will compress the I/O logs as it goes, to keep the
        memory footprint lower. When a log reaches the specified size, that chunk is
        removed and compressed in the background. Given that I/O logs are fairly
        highly compressible, this yields a nice memory savings for longer runs. The
        downside is that the compression will consume some background CPU cycles, so
        it may impact the run. This, however, is also true if the logging ends up
        consuming most of the system memory.  So pick your poison. The I/O logs are
        saved normally at the end of a run, by decompressing the chunks and storing
        them in the specified log file. This feature depends on the availability of
        zlib.

.. option:: log_compression_cpus=str

        Define the set of CPUs that are allowed to handle online log compression for
        the I/O jobs. This can provide better isolation between performance
        sensitive jobs, and background compression work. See
        :option:`cpus_allowed` for the format used.

.. option:: log_store_compressed=bool

        If set, fio will store the log files in a compressed format. They can be
        decompressed with fio, using the :option:`--inflate-log` command line
        parameter. The files will be stored with a :file:`.fz` suffix.

.. option:: log_unix_epoch=bool

        If set, fio will log Unix timestamps to the log files produced by enabling
        write_type_log for each log type, instead of the default zero-based
        timestamps.

.. option:: log_alternate_epoch=bool

        If set, fio will log timestamps based on the epoch used by the clock specified
        in the log_alternate_epoch_clock_id option, to the log files produced by
        enabling write_type_log for each log type, instead of the default zero-based
        timestamps.

.. option:: log_alternate_epoch_clock_id=int

        Specifies the clock_id to be used by clock_gettime to obtain the alternate epoch
        if either log_unix_epoch or log_alternate_epoch are true. Otherwise has no
        effect. Default value is 0, or CLOCK_REALTIME.

.. option:: block_error_percentiles=bool

        If set, record errors in trim block-sized units from writes and trims and
        output a histogram of how many trims it took to get to errors, and what kind
        of error was encountered.

.. option:: bwavgtime=int

        Average the calculated bandwidth over the given time. Value is specified in
        milliseconds. If the job also does bandwidth logging through
        :option:`write_bw_log`, then the minimum of this option and
        :option:`log_avg_msec` will be used.  Default: 500ms.

.. option:: iopsavgtime=int

        Average the calculated IOPS over the given time. Value is specified in
        milliseconds. If the job also does IOPS logging through
        :option:`write_iops_log`, then the minimum of this option and
        :option:`log_avg_msec` will be used.  Default: 500ms.

.. option:: disk_util=bool

        Generate disk utilization statistics, if the platform supports it.
        Default: true.

.. option:: disable_lat=bool

        Disable measurements of total latency numbers. Useful only for cutting back
        the number of calls to :manpage:`gettimeofday(2)`, as that does impact
        performance at really high IOPS rates.  Note that to really get rid of a
        large amount of these calls, this option must be used with
        :option:`disable_slat` and :option:`disable_bw_measurement` as well.

.. option:: disable_clat=bool

        Disable measurements of completion latency numbers. See
        :option:`disable_lat`.

.. option:: disable_slat=bool

        Disable measurements of submission latency numbers. See
        :option:`disable_lat`.

.. option:: disable_bw_measurement=bool, disable_bw=bool

        Disable measurements of throughput/bandwidth numbers. See
        :option:`disable_lat`.

.. option:: slat_percentiles=bool

        Report submission latency percentiles. Submission latency is not recorded
        for synchronous ioengines.

.. option:: clat_percentiles=bool

        Report completion latency percentiles.

.. option:: lat_percentiles=bool

        Report total latency percentiles. Total latency is the sum of submission
        latency and completion latency.

.. option:: percentile_list=float_list

        Overwrite the default list of percentiles for latencies and the block error
        histogram.  Each number is a floating point number in the range (0,100], and
        the maximum length of the list is 20. Use ``:`` to separate the numbers. For
        example, ``--percentile_list=99.5:99.9`` will cause fio to report the
        latency durations below which 99.5% and 99.9% of the observed latencies fell,
        respectively.

.. option:: significant_figures=int

        If using :option:`--output-format` of `normal`, set the significant
        figures to this value. Higher values will yield more precise IOPS and
        throughput units, while lower values will round. Requires a minimum
        value of 1 and a maximum value of 10. Defaults to 4.


Error handling
~~~~~~~~~~~~~~

.. option:: exitall_on_error

        When one job finishes in error, terminate the rest. The default is to wait
        for each job to finish.

.. option:: continue_on_error=str

        Normally fio will exit the job on the first observed failure. If this option
        is set, fio will continue the job when there is a 'non-fatal error' (EIO or
        EILSEQ) until the runtime is exceeded or the I/O size specified is
        completed. If this option is used, there are two more stats that are
        appended, the total error count and the first error. The error field given
        in the stats is the first error that was hit during the run.

        Note: a write error from the device may go unnoticed by fio when using
        buffered IO, as the write() (or similar) system call merely dirties the
        kernel pages, unless :option:`sync` or :option:`direct` is used. Device IO
        errors occur when the dirty data is actually written out to disk. If fully
        sync writes aren't desirable, :option:`fsync` or :option:`fdatasync` can be
        used as well. This is specific to writes, as reads are always synchronous.

        The allowed values are:

                **none**
                        Exit on any I/O or verify errors.

                **read**
                        Continue on read errors, exit on all others.

                **write**
                        Continue on write errors, exit on all others.

                **io**
                        Continue on any I/O error, exit on all others.

                **verify**
                        Continue on verify errors, exit on all others.

                **all**
                        Continue on all errors.

                **0**
                        Backward-compatible alias for 'none'.

                **1**
                        Backward-compatible alias for 'all'.

.. option:: ignore_error=str

        Sometimes you want to ignore some errors during test in that case you can
        specify error list for each error type, instead of only being able to
        ignore the default 'non-fatal error' using :option:`continue_on_error`.
        ``ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST`` errors for
        given error type is separated with ':'. Error may be symbol ('ENOSPC',
        'ENOMEM') or integer.  Example::

                ignore_error=EAGAIN,ENOSPC:122

        This option will ignore EAGAIN from READ, and ENOSPC and 122(EDQUOT) from
        WRITE. This option works by overriding :option:`continue_on_error` with
        the list of errors for each error type if any.

.. option:: error_dump=bool

        If set dump every error even if it is non fatal, true by default. If
        disabled only fatal error will be dumped.

Running predefined workloads
----------------------------

Fio includes predefined profiles that mimic the I/O workloads generated by
other tools.

.. option:: profile=str

        The predefined workload to run.  Current profiles are:

                **tiobench**
                        Threaded I/O bench (tiotest/tiobench) like workload.

                **act**
                        Aerospike Certification Tool (ACT) like workload.

To view a profile's additional options use :option:`--cmdhelp` after specifying
the profile.  For example::

        $ fio --profile=act --cmdhelp

Act profile options
~~~~~~~~~~~~~~~~~~~

.. option:: device-names=str
        :noindex:

        Devices to use.

.. option:: load=int
        :noindex:

        ACT load multiplier.  Default: 1.

.. option:: test-duration=time
        :noindex:

        How long the entire test takes to run.  When the unit is omitted, the value
        is given in seconds.  Default: 24h.

.. option:: threads-per-queue=int
        :noindex:

        Number of read I/O threads per device.  Default: 8.

.. option:: read-req-num-512-blocks=int
        :noindex:

        Number of 512B blocks to read at the time.  Default: 3.

.. option:: large-block-op-kbytes=int
        :noindex:

        Size of large block ops in KiB (writes).  Default: 131072.

.. option:: prep
        :noindex:

        Set to run ACT prep phase.

Tiobench profile options
~~~~~~~~~~~~~~~~~~~~~~~~

.. option:: size=str
        :noindex:

        Size in MiB.

.. option:: block=int
        :noindex:

        Block size in bytes.  Default: 4096.

.. option:: numruns=int
        :noindex:

        Number of runs.

.. option:: dir=str
        :noindex:

        Test directory.

.. option:: threads=int
        :noindex:

        Number of threads.

Interpreting the output
-----------------------

..
        Example output was based on the following:
        TZ=UTC fio --iodepth=8 --ioengine=null --size=100M --time_based \
                --rate=1256k --bs=14K --name=quick --runtime=1s --name=mixed \
                --runtime=2m --rw=rw

Fio spits out a lot of output. While running, fio will display the status of the
jobs created. An example of that would be::

    Jobs: 1 (f=1): [_(1),M(1)][24.8%][r=20.5MiB/s,w=23.5MiB/s][r=82,w=94 IOPS][eta 01m:31s]

The characters inside the first set of square brackets denote the current status of
each thread.  The first character is the first job defined in the job file, and so
forth.  The possible values (in typical life cycle order) are:

+------+-----+-----------------------------------------------------------+
| Idle | Run |                                                           |
+======+=====+===========================================================+
| P    |     | Thread setup, but not started.                            |
+------+-----+-----------------------------------------------------------+
| C    |     | Thread created.                                           |
+------+-----+-----------------------------------------------------------+
| I    |     | Thread initialized, waiting or generating necessary data. |
+------+-----+-----------------------------------------------------------+
|      |  p  | Thread running pre-reading file(s).                       |
+------+-----+-----------------------------------------------------------+
|      |  /  | Thread is in ramp period.                                 |
+------+-----+-----------------------------------------------------------+
|      |  R  | Running, doing sequential reads.                          |
+------+-----+-----------------------------------------------------------+
|      |  r  | Running, doing random reads.                              |
+------+-----+-----------------------------------------------------------+
|      |  W  | Running, doing sequential writes.                         |
+------+-----+-----------------------------------------------------------+
|      |  w  | Running, doing random writes.                             |
+------+-----+-----------------------------------------------------------+
|      |  M  | Running, doing mixed sequential reads/writes.             |
+------+-----+-----------------------------------------------------------+
|      |  m  | Running, doing mixed random reads/writes.                 |
+------+-----+-----------------------------------------------------------+
|      |  D  | Running, doing sequential trims.                          |
+------+-----+-----------------------------------------------------------+
|      |  d  | Running, doing random trims.                              |
+------+-----+-----------------------------------------------------------+
|      |  F  | Running, currently waiting for :manpage:`fsync(2)`.       |
+------+-----+-----------------------------------------------------------+
|      |  V  | Running, doing verification of written data.              |
+------+-----+-----------------------------------------------------------+
| f    |     | Thread finishing.                                         |
+------+-----+-----------------------------------------------------------+
| E    |     | Thread exited, not reaped by main thread yet.             |
+------+-----+-----------------------------------------------------------+
| _    |     | Thread reaped.                                            |
+------+-----+-----------------------------------------------------------+
| X    |     | Thread reaped, exited with an error.                      |
+------+-----+-----------------------------------------------------------+
| K    |     | Thread reaped, exited due to signal.                      |
+------+-----+-----------------------------------------------------------+

..
        Example output was based on the following:
        TZ=UTC fio --iodepth=8 --ioengine=null --size=100M --runtime=58m \
                --time_based --rate=2512k --bs=256K --numjobs=10 \
                --name=readers --rw=read --name=writers --rw=write

Fio will condense the thread string as not to take up more space on the command
line than needed. For instance, if you have 10 readers and 10 writers running,
the output would look like this::

    Jobs: 20 (f=20): [R(10),W(10)][4.0%][r=20.5MiB/s,w=23.5MiB/s][r=82,w=94 IOPS][eta 57m:36s]

Note that the status string is displayed in order, so it's possible to tell which of
the jobs are currently doing what.  In the example above this means that jobs 1--10
are readers and 11--20 are writers.

The other values are fairly self explanatory -- number of threads currently
running and doing I/O, the number of currently open files (f=), the estimated
completion percentage, the rate of I/O since last check (read speed listed first,
then write speed and optionally trim speed) in terms of bandwidth and IOPS,
and time to completion for the current running group. It's impossible to estimate
runtime of the following groups (if any).

..
        Example output was based on the following:
        TZ=UTC fio --iodepth=16 --ioengine=posixaio --filename=/tmp/fiofile \
                --direct=1 --size=100M --time_based --runtime=50s --rate_iops=89 \
                --bs=7K --name=Client1 --rw=write

When fio is done (or interrupted by :kbd:`Ctrl-C`), it will show the data for
each thread, group of threads, and disks in that order. For each overall thread (or
group) the output looks like::

        Client1: (groupid=0, jobs=1): err= 0: pid=16109: Sat Jun 24 12:07:54 2017
          write: IOPS=88, BW=623KiB/s (638kB/s)(30.4MiB/50032msec)
            slat (nsec): min=500, max=145500, avg=8318.00, stdev=4781.50
            clat (usec): min=170, max=78367, avg=4019.02, stdev=8293.31
             lat (usec): min=174, max=78375, avg=4027.34, stdev=8291.79
            clat percentiles (usec):
             |  1.00th=[  302],  5.00th=[  326], 10.00th=[  343], 20.00th=[  363],
             | 30.00th=[  392], 40.00th=[  404], 50.00th=[  416], 60.00th=[  445],
             | 70.00th=[  816], 80.00th=[ 6718], 90.00th=[12911], 95.00th=[21627],
             | 99.00th=[43779], 99.50th=[51643], 99.90th=[68682], 99.95th=[72877],
             | 99.99th=[78119]
           bw (  KiB/s): min=  532, max=  686, per=0.10%, avg=622.87, stdev=24.82, samples=  100
           iops        : min=   76, max=   98, avg=88.98, stdev= 3.54, samples=  100
          lat (usec)   : 250=0.04%, 500=64.11%, 750=4.81%, 1000=2.79%
          lat (msec)   : 2=4.16%, 4=1.84%, 10=4.90%, 20=11.33%, 50=5.37%
          lat (msec)   : 100=0.65%
          cpu          : usr=0.27%, sys=0.18%, ctx=12072, majf=0, minf=21
          IO depths    : 1=85.0%, 2=13.1%, 4=1.8%, 8=0.1%, 16=0.0%, 32=0.0%, >=64=0.0%
             submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
             complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
             issued rwt: total=0,4450,0, short=0,0,0, dropped=0,0,0
             latency   : target=0, window=0, percentile=100.00%, depth=8

The job name (or first job's name when using :option:`group_reporting`) is printed,
along with the group id, count of jobs being aggregated, last error id seen (which
is 0 when there are no errors), pid/tid of that thread and the time the job/group
completed.  Below are the I/O statistics for each data direction performed (showing
writes in the example above).  In the order listed, they denote:

**read/write/trim**
                The string before the colon shows the I/O direction the statistics
                are for.  **IOPS** is the average I/Os performed per second.  **BW**
                is the average bandwidth rate shown as: value in power of 2 format
                (value in power of 10 format).  The last two values show: (**total
                I/O performed** in power of 2 format / **runtime** of that thread).

**slat**
                Submission latency (**min** being the minimum, **max** being the
                maximum, **avg** being the average, **stdev** being the standard
                deviation).  This is the time from when fio initialized the I/O
                to submission.  For synchronous ioengines this includes the time
                up until just before the ioengine's queue function is called.
                For asynchronous ioengines this includes the time up through the
                completion of the ioengine's queue function (and commit function
                if it is defined). For sync I/O this row is not displayed as the
                slat is negligible.  This value can be in nanoseconds,
                microseconds or milliseconds --- fio will choose the most
                appropriate base and print that (in the example above
                nanoseconds was the best scale).  Note: in :option:`--minimal`
                mode latencies are always expressed in microseconds.

**clat**
                Completion latency. Same names as slat, this denotes the time from
                submission to completion of the I/O pieces. For sync I/O, this
                represents the time from when the I/O was submitted to the
                operating system to when it was completed. For asynchronous
                ioengines this is the time from when the ioengine's queue (and
                commit if available) functions were completed to when the I/O's
                completion was reaped by fio.

**lat**
                Total latency. Same names as slat and clat, this denotes the time from
                when fio created the I/O unit to completion of the I/O operation.
                It is the sum of submission and completion latency.

**bw**
                Bandwidth statistics based on samples. Same names as the xlat stats,
                but also includes the number of samples taken (**samples**) and an
                approximate percentage of total aggregate bandwidth this thread
                received in its group (**per**). This last value is only really
                useful if the threads in this group are on the same disk, since they
                are then competing for disk access.

**iops**
                IOPS statistics based on samples. Same names as bw.

**lat (nsec/usec/msec)**
                The distribution of I/O completion latencies. This is the time from when
                I/O leaves fio and when it gets completed. Unlike the separate
                read/write/trim sections above, the data here and in the remaining
                sections apply to all I/Os for the reporting group. 250=0.04% means that
                0.04% of the I/Os completed in under 250us. 500=64.11% means that 64.11%
                of the I/Os required 250 to 499us for completion.

**cpu**
                CPU usage. User and system time, along with the number of context
                switches this thread went through, usage of system and user time, and
                finally the number of major and minor page faults. The CPU utilization
                numbers are averages for the jobs in that reporting group, while the
                context and fault counters are summed.

**IO depths**
                The distribution of I/O depths over the job lifetime.  The numbers are
                divided into powers of 2 and each entry covers depths from that value
                up to those that are lower than the next entry -- e.g., 16= covers
                depths from 16 to 31.  Note that the range covered by a depth
                distribution entry can be different to the range covered by the
                equivalent submit/complete distribution entry.

**IO submit**
                How many pieces of I/O were submitting in a single submit call. Each
                entry denotes that amount and below, until the previous entry -- e.g.,
                16=100% means that we submitted anywhere between 9 to 16 I/Os per submit
                call.  Note that the range covered by a submit distribution entry can
                be different to the range covered by the equivalent depth distribution
                entry.

**IO complete**
                Like the above submit number, but for completions instead.

**IO issued rwt**
                The number of read/write/trim requests issued, and how many of them were
                short or dropped.

**IO latency**
                These values are for :option:`latency_target` and related options. When
                these options are engaged, this section describes the I/O depth required
                to meet the specified latency target.

..
        Example output was based on the following:
        TZ=UTC fio --ioengine=null --iodepth=2 --size=100M --numjobs=2 \
                --rate_process=poisson --io_limit=32M --name=read --bs=128k \
                --rate=11M --name=write --rw=write --bs=2k --rate=700k

After each client has been listed, the group statistics are printed. They
will look like this::

    Run status group 0 (all jobs):
       READ: bw=20.9MiB/s (21.9MB/s), 10.4MiB/s-10.8MiB/s (10.9MB/s-11.3MB/s), io=64.0MiB (67.1MB), run=2973-3069msec
      WRITE: bw=1231KiB/s (1261kB/s), 616KiB/s-621KiB/s (630kB/s-636kB/s), io=64.0MiB (67.1MB), run=52747-53223msec

For each data direction it prints:

**bw**
                Aggregate bandwidth of threads in this group followed by the
                minimum and maximum bandwidth of all the threads in this group.
                Values outside of brackets are power-of-2 format and those
                within are the equivalent value in a power-of-10 format.
**io**
                Aggregate I/O performed of all threads in this group. The
                format is the same as bw.
**run**
                The smallest and longest runtimes of the threads in this group.

And finally, the disk statistics are printed. This is Linux specific. They will look like this::

  Disk stats (read/write):
    sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%

Each value is printed for both reads and writes, with reads first. The
numbers denote:

**ios**
                Number of I/Os performed by all groups.
**merge**
                Number of merges performed by the I/O scheduler.
**ticks**
                Number of ticks we kept the disk busy.
**in_queue**
                Total time spent in the disk queue.
**util**
                The disk utilization. A value of 100% means we kept the disk
                busy constantly, 50% would be a disk idling half of the time.

It is also possible to get fio to dump the current output while it is running,
without terminating the job. To do that, send fio the **USR1** signal.  You can
also get regularly timed dumps by using the :option:`--status-interval`
parameter, or by creating a file in :file:`/tmp` named
:file:`fio-dump-status`. If fio sees this file, it will unlink it and dump the
current output status.


Terse output
------------

For scripted usage where you typically want to generate tables or graphs of the
results, fio can output the results in a semicolon separated format.  The format
is one long line of values, such as::

    2;card0;0;0;7139336;121836;60004;1;10109;27.932460;116.933948;220;126861;3495.446807;1085.368601;226;126864;3523.635629;1089.012448;24063;99944;50.275485%;59818.274627;5540.657370;7155060;122104;60004;1;8338;29.086342;117.839068;388;128077;5032.488518;1234.785715;391;128085;5061.839412;1236.909129;23436;100928;50.287926%;59964.832030;5644.844189;14.595833%;19.394167%;123706;0;7313;0.1%;0.1%;0.1%;0.1%;0.1%;0.1%;100.0%;0.00%;0.00%;0.00%;0.00%;0.00%;0.00%;0.01%;0.02%;0.05%;0.16%;6.04%;40.40%;52.68%;0.64%;0.01%;0.00%;0.01%;0.00%;0.00%;0.00%;0.00%;0.00%
    A description of this job goes here.

The job description (if provided) follows on a second line for terse v2.
It appears on the same line for other terse versions.

To enable terse output, use the :option:`--minimal` or
:option:`--output-format`\=terse command line options. The
first value is the version of the terse output format. If the output has to be
changed for some reason, this number will be incremented by 1 to signify that
change.

Split up, the format is as follows (comments in brackets denote when a
field was introduced or whether it's specific to some terse version):

    ::

        terse version, fio version [v3], jobname, groupid, error

    READ status::

        Total IO (KiB), bandwidth (KiB/sec), IOPS, runtime (msec)
        Submission latency: min, max, mean, stdev (usec)
        Completion latency: min, max, mean, stdev (usec)
        Completion latency percentiles: 20 fields (see below)
        Total latency: min, max, mean, stdev (usec)
        Bw (KiB/s): min, max, aggregate percentage of total, mean, stdev, number of samples [v5]
        IOPS [v5]: min, max, mean, stdev, number of samples

    WRITE status:

    ::

        Total IO (KiB), bandwidth (KiB/sec), IOPS, runtime (msec)
        Submission latency: min, max, mean, stdev (usec)
        Completion latency: min, max, mean, stdev (usec)
        Completion latency percentiles: 20 fields (see below)
        Total latency: min, max, mean, stdev (usec)
        Bw (KiB/s): min, max, aggregate percentage of total, mean, stdev, number of samples [v5]
        IOPS [v5]: min, max, mean, stdev, number of samples

    TRIM status [all but version 3]:

        Fields are similar to READ/WRITE status.

    CPU usage::

        user, system, context switches, major faults, minor faults

    I/O depths::

        <=1, 2, 4, 8, 16, 32, >=64

    I/O latencies microseconds::

        <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000

    I/O latencies milliseconds::

        <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, 2000, >=2000

    Disk utilization [v3]::

        disk name, read ios, write ios, read merges, write merges, read ticks, write ticks,
        time spent in queue, disk utilization percentage

    Additional Info (dependent on continue_on_error, default off)::

        total # errors, first error code

    Additional Info (dependent on description being set)::

        Text description

Completion latency percentiles can be a grouping of up to 20 sets, so for the
terse output fio writes all of them. Each field will look like this::

        1.00%=6112

which is the Xth percentile, and the `usec` latency associated with it.

For `Disk utilization`, all disks used by fio are shown. So for each disk there
will be a disk utilization section.

Below is a single line containing short names for each of the fields in the
minimal output v3, separated by semicolons::

        terse_version_3;fio_version;jobname;groupid;error;read_kb;read_bandwidth_kb;read_iops;read_runtime_ms;read_slat_min_us;read_slat_max_us;read_slat_mean_us;read_slat_dev_us;read_clat_min_us;read_clat_max_us;read_clat_mean_us;read_clat_dev_us;read_clat_pct01;read_clat_pct02;read_clat_pct03;read_clat_pct04;read_clat_pct05;read_clat_pct06;read_clat_pct07;read_clat_pct08;read_clat_pct09;read_clat_pct10;read_clat_pct11;read_clat_pct12;read_clat_pct13;read_clat_pct14;read_clat_pct15;read_clat_pct16;read_clat_pct17;read_clat_pct18;read_clat_pct19;read_clat_pct20;read_tlat_min_us;read_lat_max_us;read_lat_mean_us;read_lat_dev_us;read_bw_min_kb;read_bw_max_kb;read_bw_agg_pct;read_bw_mean_kb;read_bw_dev_kb;write_kb;write_bandwidth_kb;write_iops;write_runtime_ms;write_slat_min_us;write_slat_max_us;write_slat_mean_us;write_slat_dev_us;write_clat_min_us;write_clat_max_us;write_clat_mean_us;write_clat_dev_us;write_clat_pct01;write_clat_pct02;write_clat_pct03;write_clat_pct04;write_clat_pct05;write_clat_pct06;write_clat_pct07;write_clat_pct08;write_clat_pct09;write_clat_pct10;write_clat_pct11;write_clat_pct12;write_clat_pct13;write_clat_pct14;write_clat_pct15;write_clat_pct16;write_clat_pct17;write_clat_pct18;write_clat_pct19;write_clat_pct20;write_tlat_min_us;write_lat_max_us;write_lat_mean_us;write_lat_dev_us;write_bw_min_kb;write_bw_max_kb;write_bw_agg_pct;write_bw_mean_kb;write_bw_dev_kb;cpu_user;cpu_sys;cpu_csw;cpu_mjf;cpu_minf;iodepth_1;iodepth_2;iodepth_4;iodepth_8;iodepth_16;iodepth_32;iodepth_64;lat_2us;lat_4us;lat_10us;lat_20us;lat_50us;lat_100us;lat_250us;lat_500us;lat_750us;lat_1000us;lat_2ms;lat_4ms;lat_10ms;lat_20ms;lat_50ms;lat_100ms;lat_250ms;lat_500ms;lat_750ms;lat_1000ms;lat_2000ms;lat_over_2000ms;disk_name;disk_read_iops;disk_write_iops;disk_read_merges;disk_write_merges;disk_read_ticks;write_ticks;disk_queue_time;disk_util

In client/server mode terse output differs from what appears when jobs are run
locally. Disk utilization data is omitted from the standard terse output and
for v3 and later appears on its own separate line at the end of each terse
reporting cycle.


JSON output
------------

The `json` output format is intended to be both human readable and convenient
for automated parsing. For the most part its sections mirror those of the
`normal` output. The `runtime` value is reported in msec and the `bw` value is
reported in 1024 bytes per second units.


JSON+ output
------------

The `json+` output format is identical to the `json` output format except that it
adds a full dump of the completion latency bins. Each `bins` object contains a
set of (key, value) pairs where keys are latency durations and values count how
many I/Os had completion latencies of the corresponding duration. For example,
consider:

        "bins" : { "87552" : 1, "89600" : 1, "94720" : 1, "96768" : 1, "97792" : 1, "99840" : 1, "100864" : 2, "103936" : 6, "104960" : 534, "105984" : 5995, "107008" : 7529, ... }

This data indicates that one I/O required 87,552ns to complete, two I/Os required
100,864ns to complete, and 7529 I/Os required 107,008ns to complete.

Also included with fio is a Python script `fio_jsonplus_clat2csv` that takes
json+ output and generates CSV-formatted latency data suitable for plotting.

The latency durations actually represent the midpoints of latency intervals.
For details refer to :file:`stat.h`.


Trace file format
-----------------

There are two trace file format that you can encounter. The older (v1) format is
unsupported since version 1.20-rc3 (March 2008). It will still be described
below in case that you get an old trace and want to understand it.

In any case the trace is a simple text file with a single action per line.


Trace file format v1
~~~~~~~~~~~~~~~~~~~~

Each line represents a single I/O action in the following format::

        rw, offset, length

where `rw=0/1` for read/write, and the `offset` and `length` entries being in bytes.

This format is not supported in fio versions >= 1.20-rc3.


Trace file format v2
~~~~~~~~~~~~~~~~~~~~

The second version of the trace file format was added in fio version 1.17.  It
allows one to access more than one file per trace and has a bigger set of possible
file actions.

The first line of the trace file has to be::

    fio version 2 iolog

Following this can be lines in two different formats, which are described below.

The file management format::

    filename action

The `filename` is given as an absolute path. The `action` can be one of these:

**add**
                Add the given `filename` to the trace.
**open**
                Open the file with the given `filename`. The `filename` has to have
                been added with the **add** action before.
**close**
                Close the file with the given `filename`. The file has to have been
                opened before.


The file I/O action format::

    filename action offset length

The `filename` is given as an absolute path, and has to have been added and
opened before it can be used with this format. The `offset` and `length` are
given in bytes. The `action` can be one of these:

**wait**
           Wait for `offset` microseconds. Everything below 100 is discarded.
           The time is relative to the previous `wait` statement. Note that
           action `wait` is not allowed as of version 3, as the same behavior
           can be achieved using timestamps.
**read**
           Read `length` bytes beginning from `offset`.
**write**
           Write `length` bytes beginning from `offset`.
**sync**
           :manpage:`fsync(2)` the file.
**datasync**
           :manpage:`fdatasync(2)` the file.
**trim**
           Trim the given file from the given `offset` for `length` bytes.


Trace file format v3
~~~~~~~~~~~~~~~~~~~~

The third version of the trace file format was added in fio version 3.31. It
forces each action to have a timestamp associated with it.

The first line of the trace file has to be::

    fio version 3 iolog

Following this can be lines in two different formats, which are described below.

The file management format::

    timestamp filename action

The file I/O action format::

    timestamp filename action offset length

The `timestamp` is relative to the beginning of the run (ie starts at 0). The
`filename`, `action`, `offset` and `length`  are identical to version 2, except
that version 3 does not allow the `wait` action.


I/O Replay - Merging Traces
---------------------------

Colocation is a common practice used to get the most out of a machine.
Knowing which workloads play nicely with each other and which ones don't is
a much harder task. While fio can replay workloads concurrently via multiple
jobs, it leaves some variability up to the scheduler making results harder to
reproduce. Merging is a way to make the order of events consistent.

Merging is integrated into I/O replay and done when a
:option:`merge_blktrace_file` is specified. The list of files passed to
:option:`read_iolog` go through the merge process and output a single file
stored to the specified file. The output file is passed on as if it were the
only file passed to :option:`read_iolog`. An example would look like::

        $ fio --read_iolog="<file1>:<file2>" --merge_blktrace_file="<output_file>"

Creating only the merged file can be done by passing the command line argument
:option:`--merge-blktrace-only`.

Scaling traces can be done to see the relative impact of any particular trace
being slowed down or sped up. :option:`merge_blktrace_scalars` takes in a colon
separated list of percentage scalars. It is index paired with the files passed
to :option:`read_iolog`.

With scaling, it may be desirable to match the running time of all traces.
This can be done with :option:`merge_blktrace_iters`. It is index paired with
:option:`read_iolog` just like :option:`merge_blktrace_scalars`.

In an example, given two traces, A and B, each 60s long. If we want to see
the impact of trace A issuing IOs twice as fast and repeat trace A over the
runtime of trace B, the following can be done::

        $ fio --read_iolog="<trace_a>:"<trace_b>" --merge_blktrace_file"<output_file>" --merge_blktrace_scalars="50:100" --merge_blktrace_iters="2:1"

This runs trace A at 2x the speed twice for approximately the same runtime as
a single run of trace B.


CPU idleness profiling
----------------------

In some cases, we want to understand CPU overhead in a test. For example, we
test patches for the specific goodness of whether they reduce CPU usage.
Fio implements a balloon approach to create a thread per CPU that runs at idle
priority, meaning that it only runs when nobody else needs the cpu.
By measuring the amount of work completed by the thread, idleness of each CPU
can be derived accordingly.

An unit work is defined as touching a full page of unsigned characters. Mean and
standard deviation of time to complete an unit work is reported in "unit work"
section. Options can be chosen to report detailed percpu idleness or overall
system idleness by aggregating percpu stats.


Verification and triggers
-------------------------

Fio is usually run in one of two ways, when data verification is done. The first
is a normal write job of some sort with verify enabled. When the write phase has
completed, fio switches to reads and verifies everything it wrote. The second
model is running just the write phase, and then later on running the same job
(but with reads instead of writes) to repeat the same I/O patterns and verify
the contents. Both of these methods depend on the write phase being completed,
as fio otherwise has no idea how much data was written.

With verification triggers, fio supports dumping the current write state to
local files. Then a subsequent read verify workload can load this state and know
exactly where to stop. This is useful for testing cases where power is cut to a
server in a managed fashion, for instance.

A verification trigger consists of two things:

1) Storing the write state of each job.
2) Executing a trigger command.

The write state is relatively small, on the order of hundreds of bytes to single
kilobytes. It contains information on the number of completions done, the last X
completions, etc.

A trigger is invoked either through creation ('touch') of a specified file in
the system, or through a timeout setting. If fio is run with
:option:`--trigger-file`\= :file:`/tmp/trigger-file`, then it will continually
check for the existence of :file:`/tmp/trigger-file`. When it sees this file, it
will fire off the trigger (thus saving state, and executing the trigger
command).

For client/server runs, there's both a local and remote trigger. If fio is
running as a server backend, it will send the job states back to the client for
safe storage, then execute the remote trigger, if specified. If a local trigger
is specified, the server will still send back the write state, but the client
will then execute the trigger.

Verification trigger example
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Let's say we want to run a powercut test on the remote Linux machine 'server'.
Our write workload is in :file:`write-test.fio`. We want to cut power to 'server' at
some point during the run, and we'll run this test from the safety or our local
machine, 'localbox'. On the server, we'll start the fio backend normally::

        server# fio --server

and on the client, we'll fire off the workload::

        localbox$ fio --client=server --trigger-file=/tmp/my-trigger --trigger-remote="bash -c \"echo b > /proc/sysrq-triger\""

We set :file:`/tmp/my-trigger` as the trigger file, and we tell fio to execute::

        echo b > /proc/sysrq-trigger

on the server once it has received the trigger and sent us the write state. This
will work, but it's not **really** cutting power to the server, it's merely
abruptly rebooting it. If we have a remote way of cutting power to the server
through IPMI or similar, we could do that through a local trigger command
instead. Let's assume we have a script that does IPMI reboot of a given hostname,
ipmi-reboot. On localbox, we could then have run fio with a local trigger
instead::

        localbox$ fio --client=server --trigger-file=/tmp/my-trigger --trigger="ipmi-reboot server"

For this case, fio would wait for the server to send us the write state, then
execute ``ipmi-reboot server`` when that happened.

Loading verify state
~~~~~~~~~~~~~~~~~~~~

To load stored write state, a read verification job file must contain the
:option:`verify_state_load` option. If that is set, fio will load the previously
stored state. For a local fio run this is done by loading the files directly,
and on a client/server run, the server backend will ask the client to send the
files over and load them from there.


Log File Formats
----------------

Fio supports a variety of log file formats, for logging latencies, bandwidth,
and IOPS. The logs share a common format, which looks like this:

    *time* (`msec`), *value*, *data direction*, *block size* (`bytes`),
    *offset* (`bytes`), *command priority*

*Time* for the log entry is always in milliseconds. The *value* logged depends
on the type of log, it will be one of the following:

    **Latency log**
                Value is latency in nsecs
    **Bandwidth log**
                Value is in KiB/sec
    **IOPS log**
                Value is IOPS

*Data direction* is one of the following:

        **0**
                I/O is a READ
        **1**
                I/O is a WRITE
        **2**
                I/O is a TRIM

The entry's *block size* is always in bytes. The *offset* is the position in bytes
from the start of the file for that particular I/O. The logging of the offset can be
toggled with :option:`log_offset`.

*Command priority* is 0 for normal priority and 1 for high priority. This is controlled
by the ioengine specific :option:`cmdprio_percentage`.

Fio defaults to logging every individual I/O but when windowed logging is set
through :option:`log_avg_msec`, either the average (by default) or the maximum
(:option:`log_max_value` is set) *value* seen over the specified period of time
is recorded. Each *data direction* seen within the window period will aggregate
its values in a separate row. Further, when using windowed logging the *block
size* and *offset* entries will always contain 0.


Client/Server
-------------

Normally fio is invoked as a stand-alone application on the machine where the
I/O workload should be generated. However, the backend and frontend of fio can
be run separately i.e., the fio server can generate an I/O workload on the "Device
Under Test" while being controlled by a client on another machine.

Start the server on the machine which has access to the storage DUT::

        $ fio --server=args

where `args` defines what fio listens to. The arguments are of the form
``type,hostname`` or ``IP,port``. *type* is either ``ip`` (or ip4) for TCP/IP
v4, ``ip6`` for TCP/IP v6, or ``sock`` for a local unix domain socket.
*hostname* is either a hostname or IP address, and *port* is the port to listen
to (only valid for TCP/IP, not a local socket). Some examples:

1) ``fio --server``

   Start a fio server, listening on all interfaces on the default port (8765).

2) ``fio --server=ip:hostname,4444``

   Start a fio server, listening on IP belonging to hostname and on port 4444.

3) ``fio --server=ip6:::1,4444``

   Start a fio server, listening on IPv6 localhost ::1 and on port 4444.

4) ``fio --server=,4444``

   Start a fio server, listening on all interfaces on port 4444.

5) ``fio --server=1.2.3.4``

   Start a fio server, listening on IP 1.2.3.4 on the default port.

6) ``fio --server=sock:/tmp/fio.sock``

   Start a fio server, listening on the local socket :file:`/tmp/fio.sock`.

Once a server is running, a "client" can connect to the fio server with::

        fio <local-args> --client=<server> <remote-args> <job file(s)>

where `local-args` are arguments for the client where it is running, `server`
is the connect string, and `remote-args` and `job file(s)` are sent to the
server. The `server` string follows the same format as it does on the server
side, to allow IP/hostname/socket and port strings.

Fio can connect to multiple servers this way::

    fio --client=<server1> <job file(s)> --client=<server2> <job file(s)>

If the job file is located on the fio server, then you can tell the server to
load a local file as well. This is done by using :option:`--remote-config` ::

   fio --client=server --remote-config /path/to/file.fio

Then fio will open this local (to the server) job file instead of being passed
one from the client.

If you have many servers (example: 100 VMs/containers), you can input a pathname
of a file containing host IPs/names as the parameter value for the
:option:`--client` option.  For example, here is an example :file:`host.list`
file containing 2 hostnames::

        host1.your.dns.domain
        host2.your.dns.domain

The fio command would then be::

    fio --client=host.list <job file(s)>

In this mode, you cannot input server-specific parameters or job files -- all
servers receive the same job file.

In order to let ``fio --client`` runs use a shared filesystem from multiple
hosts, ``fio --client`` now prepends the IP address of the server to the
filename.  For example, if fio is using the directory :file:`/mnt/nfs/fio` and is
writing filename :file:`fileio.tmp`, with a :option:`--client` `hostfile`
containing two hostnames ``h1`` and ``h2`` with IP addresses 192.168.10.120 and
192.168.10.121, then fio will create two files::

        /mnt/nfs/fio/192.168.10.120.fileio.tmp
        /mnt/nfs/fio/192.168.10.121.fileio.tmp

Terse output in client/server mode will differ slightly from what is produced
when fio is run in stand-alone mode. See the terse output section for details.