debug: fix inverted logic in fio_did_warn()

[fio.git] / HOWTO

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.
	*?* or *help*
			Show available debug options.

.. option:: --parse-only

	Parse options 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=jobfile

	Convert `jobfile` to a set of command-line options.

.. option:: --readonly

	Turn on safety read-only checks, preventing writes.  The ``--readonly``
	option is an extra safety guard to prevent users from accidentally starting
	a write workload when that is not desired.  Fio will only write if
	`rw=write/randwrite/rw/randrw` is given.  This extra safety net can be used
	as an extra precaution as ``--readonly`` will also enable a write check in
	the I/O engine core to prevent writes due to unknown user space bug(s).

.. 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.

.. 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

	Set the internal smalloc pool size to `kb` in KiB.  The
	``--alloc-size`` switch allows one to use a larger pool size for smalloc.
	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 this `path` for fio state generated files.

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

	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 intepreted 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 each clone if not specified, but
	let all clones use the same if set.

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

.. 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 and backslash 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:

		**$jobname**
				The name of the worker thread or process.
		**$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:: zonesize=int

	Divide a file into zones of the specified size. See :option:`zoneskip`.

.. option:: zonerange=int

	Give size of an I/O zone.  See :option:`zoneskip`.

.. option:: zoneskip=int

	Skip the specified number of bytes when :option:`zonesize` data has been
	read. The two zone options can be used to only do I/O on zones of a file.


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 only).
		**randread**
				Random reads.
		**randwrite**
				Random writes.
		**randtrim**
				Random trims (Linux block 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.

	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=bool

	Fio normally reports statistics on a per data direction basis, meaning that
	reads, writes, and trims are accounted and reported separately. If this
	option is set fio sums the results and report them as "mixed" instead.

.. 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.

		**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 are available, **none** if not.

.. 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 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%.

.. 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.

.. 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, FreeBSD, and DragonFlyBSD 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[,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.

	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.

.. 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:: 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=bool

	Use synchronous I/O for buffered writes. For the majority of I/O engines,
	this means using O_SYNC. Default: false.

.. 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 4MiB in size. 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`. Defaults to 4MiB.  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 limited by other options
	(such as :option:`runtime`, for instance, or increased/decreased by :option:`io_size`).
	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.
	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 and limited to :option:`size` in
	total (if that is given). If not given, each created file is the same size.
	This option overrides :option:`size` in terms of file size, which means
	this value is used as a fixed size or possible range of each file.

.. 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) 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.

		**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.

		**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` and :option:`cpuchunks` 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.

		**guasi**
			The GUASI I/O engine is the Generic Userspace Asyncronous Syscall
			Interface approach to async I/O. See

			http://www.xmailserver.org/guasi-lib.html

			for more info on GUASI.

		**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.

		**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.

		**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 NVML
			libpmemblk library.

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

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

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:: 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 : [pvsync2]

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

.. 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:: 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:: 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]

		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:: 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]

	Specifies the name of the Ceph cluster.

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

	Specifies the name of the RBD.

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

	Specifies the name of the Ceph pool containing RBD.

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

	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:: skip_bad=bool : [mtd]

	Skip operations against known bad blocks.

.. option:: hdfsdirectory : [libhdfs]

	libhdfs will create chunk in this HDFS directory.

.. option:: chunk_size : [libhdfs]

	The size of the chunk to use for each file.

.. 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.

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.
	Additionally this option does not work when :option:`io_submit_mode` is set to
	offload. 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).


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` 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:: 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:: max_latency=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.

.. 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.

.. 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``).

.. 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_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 I/O offsets and lengths in a trace to this power of 2
	value.

.. option:: replay_scale=int

	Scale sector offsets down by this factor when replaying traces.


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.

.. option:: prioclass=int

	Set the I/O priority class. See man :manpage:`ionice(1)`.

.. 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:: cpus_allowed=str

	Controls the same options as :option:`cpumask`, but accepts a textual
	specification of the permitted CPUs instead. So to use CPUs 1 and 5 you
	would specify ``cpus_allowed=1,5``. This option also allows a range of CPUs
	to be specified -- say you wanted a binding to CPUs 1, 5, and 8 to 15, you
	would set ``cpus_allowed=1,5,8-15``.

.. 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 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:: 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 poicies: ``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 there is a
	'flow counter' which is used to regulate the proportion of activity between
	two or more jobs. Fio attempts to keep this flow counter near zero. The
	``flow`` parameter stands for how much should be added or subtracted to the
	flow counter on each iteration of the main I/O loop. That is, if one job has
	``flow=8`` and another job has ``flow=-1``, then there will be a roughly 1:8
	ratio in how much one runs vs the other.

.. option:: flow_watermark=int

	The maximum value that the absolute value of the flow counter is allowed to
	reach before the job must wait for a lower value of the counter.

.. option:: flow_sleep=int

	The period of time, in microseconds, to wait after the flow watermark has
	been exceeded 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
	but sometimes this is not the desired action.  Setting ``exitall`` will
	instead make fio terminate all other jobs when one job finishes.

.. 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
			fatest 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.

.. option:: verifysort=bool

	If true, fio will sort written verify blocks when it deems it faster to read
	them back in a sorted manner. This is often the case when overwriting an
	existing file, since the blocks are already laid out in the file system. You
	can ignore this option unless doing huge amounts of really fast I/O where
	the red-black tree sorting CPU time becomes significant. Default: true.

.. option:: verifysort_nr=int

	Pre-load and sort verify blocks for a read workload.

.. 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.

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.

		**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. 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_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.

.. 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:: 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:: clat_percentiles=bool

	Enable the reporting of percentiles of completion latencies.  This
	option is mutually exclusive with :option:`lat_percentiles`.

.. option:: lat_percentiles=bool

	Enable the reporting of percentiles of I/O latencies. This is similar
	to :option:`clat_percentiles`, except that this includes the
	submission latency. This option is mutually exclusive with
	:option:`clat_percentiles`.

.. option:: percentile_list=float_list

	Overwrite the default list of percentiles for completion latencies and
	the block error histogram.  Each number is a floating number in the
	range (0,100], and the maximum length of the list is 20. Use ``:`` to
	separate the numbers, and list the numbers in ascending order. For
	example, ``--percentile_list=99.5:99.9`` will cause fio to report the
	values of completion latency 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.

	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 it took to submit the I/O.  For
		sync I/O this row is not displayed as the slat is really the
		completion latency (since queue/complete is one operation there).
		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, clat will
		usually be equal (or very close) to 0, as the time from submit to
		complete is basically just CPU time (I/O has already been done, see slat
		explanation).

**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.

**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.

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;read_iops;read_runtime_ms;read_slat_min;read_slat_max;read_slat_mean;read_slat_dev;read_clat_min;read_clat_max;read_clat_mean;read_clat_dev;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;read_lat_max;read_lat_mean;read_lat_dev;read_bw_min;read_bw_max;read_bw_agg_pct;read_bw_mean;read_bw_dev;write_kb;write_bandwidth;write_iops;write_runtime_ms;write_slat_min;write_slat_max;write_slat_mean;write_slat_dev;write_clat_min;write_clat_max;write_clat_mean;write_clat_dev;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;write_lat_max;write_lat_mean;write_lat_dev;write_bw_min;write_bw_max;write_bw_agg_pct;write_bw_mean;write_bw_dev;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


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 to access more then 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.
**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.

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`)

*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 offset, 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`.

Fio defaults to logging every individual I/O.  When IOPS are logged for individual
I/Os the *value* entry will always be 1. If windowed logging is enabled through
:option:`log_avg_msec`, fio logs the average values over the specified period of time.
If windowed logging is enabled and :option:`log_max_value` is set, then fio logs
maximum values in that window instead of averages. Since *data direction*, *block
size* and *offset* are per-I/O values, if windowed logging is enabled they
aren't applicable and will be 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