Update documentation for random_distribution=gauss

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.TH fio 1 "December 2014" "User Manual"
.SH NAME
fio \- flexible I/O tester
.SH SYNOPSIS
.B fio
[\fIoptions\fR] [\fIjobfile\fR]...
.SH DESCRIPTION
.B fio
is a tool that will spawn a number of threads or processes doing a
particular type of I/O action as specified by the user.
The typical use of fio is to write a job file matching the I/O load
one wants to simulate.
.SH OPTIONS
.TP
.BI \-\-debug \fR=\fPtype
Enable verbose tracing of various fio actions. May be `all' for all types
or individual types separated by a comma (eg \-\-debug=io,file). `help' will
list all available tracing options.
.TP
.BI \-\-output \fR=\fPfilename
Write output to \fIfilename\fR.
.TP
.BI \-\-output-format \fR=\fPformat
Set the reporting format to \fInormal\fR, \fIterse\fR, \fIjson\fR, or
\fIjson+\fR. Multiple formats can be selected, separate by a comma. \fIterse\fR
is a CSV based format. \fIjson+\fR is like \fIjson\fR, except it adds a full
dump of the latency buckets.
.TP
.BI \-\-runtime \fR=\fPruntime
Limit run time to \fIruntime\fR seconds.
.TP
.B \-\-bandwidth\-log
Generate per-job bandwidth logs.
.TP
.B \-\-minimal
Print statistics in a terse, semicolon-delimited format.
.TP
.B \-\-append-terse
Print statistics in selected mode AND terse, semicolon-delimited format.
Deprecated, use \-\-output-format instead to select multiple formats.
.TP
.B \-\-version
Display version information and exit.
.TP
.BI \-\-terse\-version \fR=\fPversion
Set terse version output format (Current version 3, or older version 2).
.TP
.B \-\-help
Display usage information and exit.
.TP
.B \-\-cpuclock-test
Perform test and validation of internal CPU clock
.TP
.BI \-\-crctest[\fR=\fPtest]
Test the speed of the builtin checksumming functions. If no argument is given,
all of them are tested. Or a comma separated list can be passed, in which
case the given ones are tested.
.TP
.BI \-\-cmdhelp \fR=\fPcommand
Print help information for \fIcommand\fR.  May be `all' for all commands.
.TP
.BI \-\-enghelp \fR=\fPioengine[,command]
List all commands defined by \fIioengine\fR, or print help for \fIcommand\fR defined by \fIioengine\fR.
.TP
.BI \-\-showcmd \fR=\fPjobfile
Convert \fIjobfile\fR to a set of command-line options.
.TP
.BI \-\-eta \fR=\fPwhen
Specifies when real-time ETA estimate should be printed.  \fIwhen\fR may
be one of `always', `never' or `auto'.
.TP
.BI \-\-eta\-newline \fR=\fPtime
Force an ETA newline for every `time` period passed.
.TP
.BI \-\-status\-interval \fR=\fPtime
Report full output status every `time` period passed.
.TP
.BI \-\-readonly
Turn on safety read-only checks, preventing any attempted write.
.TP
.BI \-\-section \fR=\fPsec
Only run section \fIsec\fR from job file. This option can be used multiple times to add more sections to run.
.TP
.BI \-\-alloc\-size \fR=\fPkb
Set the internal smalloc pool size to \fIkb\fP kilobytes.
.TP
.BI \-\-warnings\-fatal
All fio parser warnings are fatal, causing fio to exit with an error.
.TP
.BI \-\-max\-jobs \fR=\fPnr
Set the maximum allowed number of jobs (threads/processes) to support.
.TP
.BI \-\-server \fR=\fPargs
Start a backend server, with \fIargs\fP specifying what to listen to. See client/server section.
.TP
.BI \-\-daemonize \fR=\fPpidfile
Background a fio server, writing the pid to the given pid file.
.TP
.BI \-\-client \fR=\fPhost
Instead of running the jobs locally, send and run them on the given host or set of hosts.  See client/server section.
.TP
.BI \-\-idle\-prof \fR=\fPoption
Report cpu idleness on a system or percpu basis (\fIoption\fP=system,percpu) or run unit work calibration only (\fIoption\fP=calibrate).
.SH "JOB FILE FORMAT"
Job files are in `ini' format. They consist of one or more
job definitions, which begin with a job name in square brackets and
extend to the next job name.  The job name can be any ASCII string
except `global', which has a special meaning.  Following the job name is
a sequence of zero or more parameters, one per line, that define the
behavior of the job.  Any line starting with a `;' or `#' character is
considered a comment and ignored.
.P
If \fIjobfile\fR is specified as `-', the job file will be read from
standard input.
.SS "Global Section"
The global section contains default parameters for jobs specified in the
job file.  A job is only affected by global sections residing above it,
and there may be any number of global sections.  Specific job definitions
may override any parameter set in global sections.
.SH "JOB PARAMETERS"
.SS Types
Some parameters may take arguments of a specific type.
Anywhere a numeric value is required, an arithmetic expression may be used,
provided it is surrounded by parentheses. Supported operators are:
.RS
.RS
.TP
.B addition (+)
.TP
.B subtraction (-)
.TP
.B multiplication (*)
.TP
.B division (/)
.TP
.B modulus (%)
.TP
.B exponentiation (^)
.RE
.RE
.P
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 types used are:
.TP
.I str
String: a sequence of alphanumeric characters.
.TP
.I int
SI integer: a whole number, possibly containing a suffix denoting the base unit
of the value.  Accepted suffixes are `k', 'M', 'G', 'T', and 'P', denoting
kilo (1024), mega (1024^2), giga (1024^3), tera (1024^4), and peta (1024^5)
respectively. If prefixed with '0x', the value is assumed to be base 16
(hexadecimal). A suffix may include a trailing 'b', for instance 'kb' is
identical to 'k'. You can specify a base 10 value by using 'KiB', 'MiB','GiB',
etc. This is useful for disk drives where values are often given in base 10
values. Specifying '30GiB' will get you 30*1000^3 bytes.
When specifying times the default suffix meaning changes, still denoting the
base unit of the value, but accepted suffixes are 'D' (days), 'H' (hours), 'M'
(minutes), 'S' Seconds, 'ms' (or msec) milli seconds, 'us' (or 'usec') micro
seconds. Time values without a unit specify seconds.
The suffixes are not case sensitive.
.TP
.I bool
Boolean: a true or false value. `0' denotes false, `1' denotes true.
.TP
.I irange
Integer range: a range of integers specified in the format
\fIlower\fR:\fIupper\fR or \fIlower\fR\-\fIupper\fR. \fIlower\fR and
\fIupper\fR may contain a suffix as described above.  If an option allows two
sets of ranges, they are separated with a `,' or `/' character. For example:
`8\-8k/8M\-4G'.
.TP
.I float_list
List of floating numbers: A list of floating numbers, separated by
a ':' character.
.SS "Parameter List"
.TP
.BI name \fR=\fPstr
May be used to override the job name.  On the command line, this parameter
has the special purpose of signalling the start of a new job.
.TP
.BI wait_for \fR=\fPstr
Specifies the name of the already defined job to wait for. Single waitee name
only may be specified. If set, the job won't be started until all workers of
the 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).
.TP
.BI description \fR=\fPstr
Human-readable description of the job. It is printed when the job is run, but
otherwise has no special purpose.
.TP
.BI directory \fR=\fPstr
Prefix filenames with this directory.  Used to place files in a location other
than `./'.
You can specify a number of directories by separating the names with a ':'
character. These directories will be assigned equally distributed to job clones
creates with \fInumjobs\fR as long as they are using generated filenames.
If specific \fIfilename(s)\fR are set fio will use the first listed directory,
and thereby matching the  \fIfilename\fR semantic which generates a file each
clone if not specified, but let all clones use the same if set. See
\fIfilename\fR for considerations regarding escaping certain characters on
some platforms.
.TP
.BI filename \fR=\fPstr
.B fio
normally makes up a file name based on the job name, thread number, and file
number. If you want to share files between threads in a job or several jobs,
specify a \fIfilename\fR for each of them to override the default.
If the I/O engine is file-based, you can specify
a number of files by separating the names with a `:' character. `\-' is a
reserved name, meaning stdin or stdout, depending on the read/write direction
set. On Windows, disk devices are accessed as \\.\PhysicalDrive0 for the first
device, \\.\PhysicalDrive1 for the second etc. Note: Windows and FreeBSD
prevent write access to areas of the disk containing in-use data
(e.g. filesystems). If the wanted filename does need to include a colon, then
escape that with a '\\' character. For instance, if the filename is
"/dev/dsk/foo@3,0:c", then you would use filename="/dev/dsk/foo@3,0\\:c".
.TP
.BI filename_format \fR=\fPstr
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
\fBjobname.jobnumber.filenumber\fP. With this option, that can be
customized. Fio will recognize and replace the following keywords in this
string:
.RS
.RS
.TP
.B $jobname
The name of the worker thread or process.
.TP
.B $jobnum
The incremental number of the worker thread or process.
.TP
.B $filenum
The incremental number of the file for that worker thread or process.
.RE
.P
To have dependent jobs share a set of files, this option can be set to
have fio generate filenames that are shared between the two. For instance,
if \fBtestfiles.$filenum\fR is specified, file number 4 for any job will
be named \fBtestfiles.4\fR. The default of \fB$jobname.$jobnum.$filenum\fR
will be used if no other format specifier is given.
.RE
.P
.TP
.BI lockfile \fR=\fPstr
Fio defaults to not locking any files before it does IO to them. If a file or
file descriptor is shared, fio can serialize IO to that file to make the end
result consistent. This is usual for emulating real workloads that share files.
The lock modes are:
.RS
.RS
.TP
.B none
No locking. This is the default.
.TP
.B exclusive
Only one thread or process may do IO at a time, excluding all others.
.TP
.B readwrite
Read-write locking on the file. Many readers may access the file at the same
time, but writes get exclusive access.
.RE
.RE
.P
.BI opendir \fR=\fPstr
Recursively open any files below directory \fIstr\fR.
.TP
.BI readwrite \fR=\fPstr "\fR,\fP rw" \fR=\fPstr
Type of I/O pattern.  Accepted values are:
.RS
.RS
.TP
.B read
Sequential reads.
.TP
.B write
Sequential writes.
.TP
.B trim
Sequential trim (Linux block devices only).
.TP
.B randread
Random reads.
.TP
.B randwrite
Random writes.
.TP
.B randtrim
Random trim (Linux block devices only).
.TP
.B rw, readwrite
Mixed sequential reads and writes.
.TP
.B randrw
Mixed random reads and writes.
.TP
.B trimwrite
Trim and write mixed workload. Blocks will be trimmed first, then the same
blocks will be written to.
.RE
.P
For mixed I/O, the default split is 50/50. For certain types of io the result
may still be skewed a bit, since the speed may be different. It is possible to
specify a number of IO's to do before getting a new offset, this is done by
appending a `:\fI<nr>\fR to the end of the string given. For a random read, it
would look like \fBrw=randread:8\fR for passing in an offset modifier with a
value of 8. If the postfix is used with a sequential IO pattern, then the value
specified will be added to the generated offset for each IO. For instance,
using \fBrw=write:4k\fR will skip 4k for every write. It turns sequential IO
into sequential IO with holes. See the \fBrw_sequencer\fR option.
.RE
.TP
.BI rw_sequencer \fR=\fPstr
If an offset modifier is given by appending a number to the \fBrw=<str>\fR line,
then this option controls how that number modifies the IO offset being
generated. Accepted values are:
.RS
.RS
.TP
.B sequential
Generate sequential offset
.TP
.B identical
Generate the same offset
.RE
.P
\fBsequential\fR is only useful for random IO, where fio would normally
generate a new random offset for every IO. If you append eg 8 to randread, you
would get a new random offset for every 8 IO's. The result would be a seek for
only every 8 IO's, instead of for every IO. Use \fBrw=randread:8\fR to specify
that. As sequential IO is already sequential, setting \fBsequential\fR for that
would not result in any differences.  \fBidentical\fR behaves in a similar
fashion, except it sends the same offset 8 number of times before generating a
new offset.
.RE
.P
.TP
.BI kb_base \fR=\fPint
The base unit for a kilobyte. The defacto base is 2^10, 1024.  Storage
manufacturers like to use 10^3 or 1000 as a base ten unit instead, for obvious
reasons. Allowed values are 1024 or 1000, with 1024 being the default.
.TP
.BI unified_rw_reporting \fR=\fPbool
Fio normally reports statistics on a per data direction basis, meaning that
read, write, and trim are accounted and reported separately. If this option is
set fio sums the results and reports them as "mixed" instead.
.TP
.BI randrepeat \fR=\fPbool
Seed the random number generator used for random I/O patterns in a predictable
way so the pattern is repeatable across runs.  Default: true.
.TP
.BI allrandrepeat \fR=\fPbool
Seed all random number generators in a predictable way so results are
repeatable across runs.  Default: false.
.TP
.BI randseed \fR=\fPint
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 \fBrandrepeat\fR setting.
.TP
.BI fallocate \fR=\fPstr
Whether pre-allocation is performed when laying down files. Accepted values
are:
.RS
.RS
.TP
.B none
Do not pre-allocate space.
.TP
.B posix
Pre-allocate via \fBposix_fallocate\fR\|(3).
.TP
.B keep
Pre-allocate via \fBfallocate\fR\|(2) with FALLOC_FL_KEEP_SIZE set.
.TP
.B 0
Backward-compatible alias for 'none'.
.TP
.B 1
Backward-compatible alias for 'posix'.
.RE
.P
May not be available on all supported platforms. 'keep' is only
available on Linux. If using ZFS on Solaris this must be set to 'none'
because ZFS doesn't support it. Default: 'posix'.
.RE
.TP
.BI fadvise_hint \fR=\fPbool
Use \fBposix_fadvise\fR\|(2) to advise the kernel what I/O patterns
are likely to be issued. Default: true.
.TP
.BI fadvise_stream \fR=\fPint
Use \fBposix_fadvise\fR\|(2) to advise the kernel what stream ID the
writes issued belong to. Only supported on Linux. Note, this option
may change going forward.
.TP
.BI size \fR=\fPint
Total size of I/O for this job.  \fBfio\fR will run until this many bytes have
been transferred, unless limited by other options (\fBruntime\fR, for instance,
or increased/descreased by \fBio_size\fR). Unless \fBnrfiles\fR and
\fBfilesize\fR options are given, this amount will be divided between the
available files for the job. If not set, 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.
.TP
.BI io_size \fR=\fPint "\fR,\fB io_limit \fR=\fPint
Normally fio operates within the region set by \fBsize\fR, which means that
the \fBsize\fR option sets both the region and size of IO to be performed.
Sometimes that is not what you want. With this option, it is possible to
define just the amount of IO that fio should do. For instance, if \fBsize\fR
is set to 20G and \fBio_limit\fR is set to 5G, fio will perform IO within
the first 20G but exit when 5G have been done. The opposite is also
possible - if \fBsize\fR is set to 20G, and \fBio_size\fR is set to 40G, then
fio will do 40G of IO within the 0..20G region.
.TP
.BI fill_device \fR=\fPbool "\fR,\fB fill_fs" \fR=\fPbool
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 IO 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.
.TP
.BI filesize \fR=\fPirange
Individual file sizes. May be a range, in which case \fBfio\fR will select sizes
for files at random within the given range, limited to \fBsize\fR in total (if
that is given). If \fBfilesize\fR is not specified, each created file is the
same size.
.TP
.BI file_append \fR=\fPbool
Perform IO 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 \fRoffset\fP to the size
of a file. This option is ignored on non-regular files.
.TP
.BI blocksize \fR=\fPint[,int] "\fR,\fB bs" \fR=\fPint[,int]
Block size for I/O units.  Default: 4k.  Values for reads, writes, and trims
can be specified separately in the format \fIread\fR,\fIwrite\fR,\fItrim\fR
either of which may be empty to leave that value at its default. If a trailing
comma isn't given, the remainder will inherit the last value set.
.TP
.BI blocksize_range \fR=\fPirange[,irange] "\fR,\fB bsrange" \fR=\fPirange[,irange]
Specify a range of I/O block sizes.  The issued I/O unit will always be a
multiple of the minimum size, unless \fBblocksize_unaligned\fR is set.  Applies
to both reads and writes if only one range is given, but can be specified
separately with a comma separating the values. Example: bsrange=1k-4k,2k-8k.
Also (see \fBblocksize\fR).
.TP
.BI bssplit \fR=\fPstr
This option allows even finer grained control of the block sizes issued,
not just even splits between them. With this option, you can weight various
block sizes for exact control of the issued IO for a job that has mixed
block sizes. The format of the option is bssplit=blocksize/percentage,
optionally adding as many definitions as needed separated by a colon.
Example: bssplit=4k/10:64k/50:32k/40 would issue 50% 64k blocks, 10% 4k
blocks and 40% 32k blocks. \fBbssplit\fR also supports giving separate
splits to reads and writes. The format is identical to what the
\fBbs\fR option accepts, the read and write parts are separated with a
comma.
.TP
.B blocksize_unaligned\fR,\fP bs_unaligned
If set, any size in \fBblocksize_range\fR may be used.  This typically won't
work with direct I/O, as that normally requires sector alignment.
.TP
.BI blockalign \fR=\fPint[,int] "\fR,\fB ba" \fR=\fPint[,int]
At what boundary to align random IO offsets. Defaults to the same as 'blocksize'
the minimum blocksize given.  Minimum alignment is typically 512b
for using direct IO, 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.
.TP
.BI bs_is_seq_rand \fR=\fPbool
If this option is set, fio will use the normal read,write blocksize settings as
sequential,random instead. Any random read or write will use the WRITE
blocksize settings, and any sequential read or write will use the READ
blocksize setting.
.TP
.B zero_buffers
Initialize buffers with all zeros. Default: fill buffers with random data.
.TP
.B refill_buffers
If this option is given, fio will refill the IO buffers on every submit. The
default is to only fill it at init time and reuse that data. Only makes sense
if zero_buffers isn't specified, naturally. If data verification is enabled,
refill_buffers is also automatically enabled.
.TP
.BI scramble_buffers \fR=\fPbool
If \fBrefill_buffers\fR is too costly and the target is using data
deduplication, then setting this option will slightly modify the IO 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.
.TP
.BI buffer_compress_percentage \fR=\fPint
If this is set, then fio will attempt to provide IO buffer content (on WRITEs)
that compress to the specified level. Fio does this by providing a mix of
random data and a fixed pattern. The fixed pattern is either zeroes, or the
pattern specified by \fBbuffer_pattern\fR. If the pattern option is used, it
might skew the compression ratio slightly. Note that this is per block size
unit, for file/disk wide compression level that matches this setting. Note
that this is per block size unit, for file/disk wide compression level that
matches this setting, you'll also want to set refill_buffers.
.TP
.BI buffer_compress_chunk \fR=\fPint
See \fBbuffer_compress_percentage\fR. This setting allows fio to manage how
big the ranges of random data and zeroed data is. Without this set, fio will
provide \fBbuffer_compress_percentage\fR of blocksize random data, followed by
the remaining zeroed. With this set to some chunk size smaller than the block
size, fio can alternate random and zeroed data throughout the IO buffer.
.TP
.BI buffer_pattern \fR=\fPstr
If set, fio will fill the IO buffers with this pattern. If not set, the contents
of IO buffers is 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
"", e.g.:
.RS
.RS
\fBbuffer_pattern\fR="abcd"
.RS
or
.RE
\fBbuffer_pattern\fR=-12
.RS
or
.RE
\fBbuffer_pattern\fR=0xdeadface
.RE
.LP
Also you can combine everything together in any order:
.LP
.RS
\fBbuffer_pattern\fR=0xdeadface"abcd"-12
.RE
.RE
.TP
.BI dedupe_percentage \fR=\fPint
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.
.TP
.BI nrfiles \fR=\fPint
Number of files to use for this job.  Default: 1.
.TP
.BI openfiles \fR=\fPint
Number of files to keep open at the same time.  Default: \fBnrfiles\fR.
.TP
.BI file_service_type \fR=\fPstr
Defines how files to service are selected.  The following types are defined:
.RS
.RS
.TP
.B random
Choose a file at random.
.TP
.B roundrobin
Round robin over opened files (default).
.TP
.B sequential
Do each file in the set sequentially.
.RE
.P
The number of I/Os to issue before switching to a new file can be specified by
appending `:\fIint\fR' to the service type.
.RE
.TP
.BI ioengine \fR=\fPstr
Defines how the job issues I/O.  The following types are defined:
.RS
.RS
.TP
.B sync
Basic \fBread\fR\|(2) or \fBwrite\fR\|(2) I/O.  \fBfseek\fR\|(2) is used to
position the I/O location.
.TP
.B psync
Basic \fBpread\fR\|(2) or \fBpwrite\fR\|(2) I/O.
.TP
.B vsync
Basic \fBreadv\fR\|(2) or \fBwritev\fR\|(2) I/O. Will emulate queuing by
coalescing adjacent IOs into a single submission.
.TP
.B pvsync
Basic \fBpreadv\fR\|(2) or \fBpwritev\fR\|(2) I/O.
.TP
.B pvsync2
Basic \fBpreadv2\fR\|(2) or \fBpwritev2\fR\|(2) I/O.
.TP
.B libaio
Linux native asynchronous I/O. This ioengine defines engine specific options.
.TP
.B posixaio
POSIX asynchronous I/O using \fBaio_read\fR\|(3) and \fBaio_write\fR\|(3).
.TP
.B solarisaio
Solaris native asynchronous I/O.
.TP
.B windowsaio
Windows native asynchronous I/O.
.TP
.B mmap
File is memory mapped with \fBmmap\fR\|(2) and data copied using
\fBmemcpy\fR\|(3).
.TP
.B splice
\fBsplice\fR\|(2) is used to transfer the data and \fBvmsplice\fR\|(2) to
transfer data from user-space to the kernel.
.TP
.B syslet-rw
Use the syslet system calls to make regular read/write asynchronous.
.TP
.B sg
SCSI generic sg v3 I/O. May be either synchronous using the SG_IO ioctl, or if
the target is an sg character device, we use \fBread\fR\|(2) and
\fBwrite\fR\|(2) for asynchronous I/O.
.TP
.B null
Doesn't transfer any data, just pretends to.  Mainly used to exercise \fBfio\fR
itself and for debugging and testing purposes.
.TP
.B net
Transfer over the network.  The protocol to be used can be defined with the
\fBprotocol\fR parameter.  Depending on the protocol, \fBfilename\fR,
\fBhostname\fR, \fBport\fR, or \fBlisten\fR must be specified.
This ioengine defines engine specific options.
.TP
.B netsplice
Like \fBnet\fR, but uses \fBsplice\fR\|(2) and \fBvmsplice\fR\|(2) to map data
and send/receive. This ioengine defines engine specific options.
.TP
.B cpuio
Doesn't transfer any data, but burns CPU cycles according to \fBcpuload\fR and
\fBcpucycles\fR parameters.
.TP
.B guasi
The GUASI I/O engine is the Generic Userspace Asynchronous Syscall Interface
approach to asynchronous I/O.
.br
See <http://www.xmailserver.org/guasi\-lib.html>.
.TP
.B 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.
.TP
.B external
Loads an external I/O engine object file.  Append the engine filename as
`:\fIenginepath\fR'.
.TP
.B falloc
   IO engine that does regular linux native fallocate call to simulate data
transfer as fio ioengine
.br
  DDIR_READ  does fallocate(,mode = FALLOC_FL_KEEP_SIZE,)
.br
  DIR_WRITE does fallocate(,mode = 0)
.br
  DDIR_TRIM does fallocate(,mode = FALLOC_FL_KEEP_SIZE|FALLOC_FL_PUNCH_HOLE)
.TP
.B e4defrag
IO engine that does regular EXT4_IOC_MOVE_EXT ioctls to simulate defragment activity
request to DDIR_WRITE event
.TP
.B rbd
IO 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.
.TP
.B gfapi
Using Glusterfs libgfapi sync interface to direct access to Glusterfs volumes without
having to go through FUSE. This ioengine defines engine specific
options.
.TP
.B 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.
.TP
.B libhdfs
Read and write through Hadoop (HDFS).  The \fBfilename\fR 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, libhdfs engine expects
bunch of small files to be created over HDFS, and engine will randomly pick a
file out of those files based on the offset generated by fio backend. (see the
example job file to create such files, use rw=write option). Please note, you
might want to set necessary environment variables to work with hdfs/libhdfs
properly.
.TP
.B mtd
Read, write and erase an MTD character device (e.g., /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 writetrim mode works well for this
constraint.
.RE
.P
.RE
.TP
.BI iodepth \fR=\fPint
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
degress when 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 \fBdirect\fR=1, since buffered IO is
not async on that OS. Keep an eye on the IO depth distribution in the
fio output to verify that the achieved depth is as expected. Default: 1.
.TP
.BI iodepth_batch \fR=\fPint "\fR,\fP iodepth_batch_submit" \fR=\fPint
This defines how many pieces of IO to submit at once. It defaults to 1
which means that we submit each IO as soon as it is available, but can
be raised to submit bigger batches of IO at the time. If it is set to 0
the \fBiodepth\fR value will be used.
.TP
.BI iodepth_batch_complete_min \fR=\fPint "\fR,\fP iodepth_batch_complete" \fR=\fPint
This defines how many pieces of IO to retrieve at once. It defaults to 1 which
 means that we'll ask for a minimum of 1 IO in the retrieval process from the
kernel. The IO retrieval will go on until we hit the limit set by
\fBiodepth_low\fR. If this variable is set to 0, then fio will always check for
completed events before queuing more IO. This helps reduce IO latency, at the
cost of more retrieval system calls.
.TP
.BI iodepth_batch_complete_max \fR=\fPint
This defines maximum pieces of IO to
retrieve at once. This variable should be used along with
\fBiodepth_batch_complete_min\fR=int variable, specifying the range
of min and max amount of IO which should be retrieved. By default
it is equal to \fBiodepth_batch_complete_min\fR value.

Example #1:
.RS
.RS
\fBiodepth_batch_complete_min\fR=1
.LP
\fBiodepth_batch_complete_max\fR=<iodepth>
.RE

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

Example #2:
.RS
\fBiodepth_batch_complete_min\fR=0
.LP
\fBiodepth_batch_complete_max\fR=<iodepth>
.RE

which means that we can retrieve up to the whole submitted
queue depth, but if none of IO has been completed yet, we will
NOT wait and immediately exit the system call. In this example
we simply do polling.
.RE
.TP
.BI iodepth_low \fR=\fPint
Low watermark indicating when to start filling the queue again.  Default:
\fBiodepth\fR.
.TP
.BI io_submit_mode \fR=\fPstr
This option controls how fio submits the IO to the IO engine. The default is
\fBinline\fR, which means that the fio job threads submit and reap IO directly.
If set to \fBoffload\fR, the job threads will offload IO submission to a
dedicated pool of IO threads. This requires some coordination and thus has a
bit of extra overhead, especially for lower queue depth IO 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 IO gets back up on the device side (the coordinated omission
problem).
.TP
.BI direct \fR=\fPbool
If true, use non-buffered I/O (usually O_DIRECT).  Default: false.
.TP
.BI atomic \fR=\fPbool
If value is true, attempt to use atomic direct IO. Atomic writes are guaranteed
to be stable once acknowledged by the operating system. Only Linux supports
O_ATOMIC right now.
.TP
.BI buffered \fR=\fPbool
If true, use buffered I/O.  This is the opposite of the \fBdirect\fR parameter.
Default: true.
.TP
.BI offset \fR=\fPint
Offset in the file to start I/O. Data before the offset will not be touched.
.TP
.BI offset_increment \fR=\fPint
If this is provided, then the real offset becomes the
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
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.
.TP
.BI number_ios \fR=\fPint
Fio will normally perform IOs until it has exhausted the size of the region
set by \fBsize\fR, 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 IOs to perform. When fio reaches this number, it will exit
normally and report status. Note that this does not extend the amount
of IO that will be done, it will only stop fio if this condition is met
before other end-of-job criteria.
.TP
.BI fsync \fR=\fPint
How many I/Os to perform before issuing an \fBfsync\fR\|(2) of dirty data.  If
0, don't sync.  Default: 0.
.TP
.BI fdatasync \fR=\fPint
Like \fBfsync\fR, but uses \fBfdatasync\fR\|(2) instead to only sync the
data parts of the file. Default: 0.
.TP
.BI write_barrier \fR=\fPint
Make every Nth write a barrier write.
.TP
.BI sync_file_range \fR=\fPstr:int
Use \fBsync_file_range\fR\|(2) for every \fRval\fP number of write operations. Fio will
track range of writes that have happened since the last \fBsync_file_range\fR\|(2) call.
\fRstr\fP can currently be one or more of:
.RS
.TP
.B wait_before
SYNC_FILE_RANGE_WAIT_BEFORE
.TP
.B write
SYNC_FILE_RANGE_WRITE
.TP
.B wait_after
SYNC_FILE_RANGE_WRITE
.TP
.RE
.P
So if you do sync_file_range=wait_before,write:8, fio would use
\fBSYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE\fP for every 8 writes.
Also see the \fBsync_file_range\fR\|(2) man page.  This option is Linux specific.
.TP
.BI overwrite \fR=\fPbool
If writing, setup the file first and do overwrites.  Default: false.
.TP
.BI end_fsync \fR=\fPbool
Sync file contents when a write stage has completed.  Default: false.
.TP
.BI fsync_on_close \fR=\fPbool
If true, sync file contents on close.  This differs from \fBend_fsync\fR in that
it will happen on every close, not just at the end of the job.  Default: false.
.TP
.BI rwmixread \fR=\fPint
Percentage of a mixed workload that should be reads. Default: 50.
.TP
.BI rwmixwrite \fR=\fPint
Percentage of a mixed workload that should be writes.  If \fBrwmixread\fR and
\fBrwmixwrite\fR are given and do not sum to 100%, the latter of the two
overrides 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.
.TP
.BI random_distribution \fR=\fPstr:float
By default, fio will use a completely uniform random distribution when asked
to perform random IO. 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:
.RS
.TP
.B random
Uniform random distribution
.TP
.B zipf
Zipf distribution
.TP
.B pareto
Pareto distribution
.TP
.B gauss
Normal (gaussian) distribution
.TP
.RE
.P
When using a \fBzipf\fR or \fBpareto\fR distribution, an input value is also
needed to define the access pattern. For \fBzipf\fR, this is the zipf theta.
For \fBpareto\fR, it's the pareto power. Fio includes a test program, genzipf,
that can be used visualize what the given input values will yield in terms of
hit rates. If you wanted to use \fBzipf\fR 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 \fBgauss\fR distribution, a
normal deviation is supplied as a value between 0 and 100.
.TP
.BI percentage_random \fR=\fPint
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. It is possible to set different values for reads, writes, and
trim. To do so, simply use a comma separated list. See \fBblocksize\fR.
.TP
.B norandommap
Normally \fBfio\fR will cover every block of the file when doing random I/O. If
this parameter is given, a new offset will be chosen without looking at past
I/O history.  This parameter is mutually exclusive with \fBverify\fR.
.TP
.BI softrandommap \fR=\fPbool
See \fBnorandommap\fR. 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.
.TP
.BI random_generator \fR=\fPstr
Fio supports the following engines for generating IO offsets for random IO:
.RS
.TP
.B tausworthe
Strong 2^88 cycle random number generator
.TP
.B lfsr
Linear feedback shift register generator
.TP
.B tausworthe64
Strong 64-bit 2^258 cycle random number generator
.TP
.RE
.P
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 IO 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.
.TP
.BI nice \fR=\fPint
Run job with given nice value.  See \fBnice\fR\|(2).
.TP
.BI prio \fR=\fPint
Set I/O priority value of this job between 0 (highest) and 7 (lowest).  See
\fBionice\fR\|(1).
.TP
.BI prioclass \fR=\fPint
Set I/O priority class.  See \fBionice\fR\|(1).
.TP
.BI thinktime \fR=\fPint
Stall job for given number of microseconds between issuing I/Os.
.TP
.BI thinktime_spin \fR=\fPint
Pretend to spend CPU time for given number of microseconds, sleeping the rest
of the time specified by \fBthinktime\fR.  Only valid if \fBthinktime\fR is set.
.TP
.BI thinktime_blocks \fR=\fPint
Only valid if thinktime is set - control how many blocks to issue, before
waiting \fBthinktime\fR microseconds. If not set, defaults to 1 which will
make fio wait \fBthinktime\fR microseconds after every block. This
effectively makes any queue depth setting redundant, since no more than 1 IO
will be queued before we have to complete it and do our thinktime. In other
words, this setting effectively caps the queue depth if the latter is larger.
Default: 1.
.TP
.BI rate \fR=\fPint
Cap bandwidth used by this job. The number is in bytes/sec, the normal postfix
rules apply. You can use \fBrate\fR=500k to limit reads and writes to 500k each,
or you can specify read and writes separately. Using \fBrate\fR=1m,500k would
limit reads to 1MB/sec and writes to 500KB/sec. Capping only reads or writes
can be done with \fBrate\fR=,500k or \fBrate\fR=500k,. The former will only
limit writes (to 500KB/sec), the latter will only limit reads.
.TP
.BI rate_min \fR=\fPint
Tell \fBfio\fR to do whatever it can to maintain at least the given bandwidth.
Failing to meet this requirement will cause the job to exit. The same format
as \fBrate\fR is used for read vs write separation.
.TP
.BI rate_iops \fR=\fPint
Cap the bandwidth to this number of IOPS. Basically the same as rate, just
specified independently of bandwidth. The same format as \fBrate\fR is used for
read vs write separation. If \fBblocksize\fR is a range, the smallest block
size is used as the metric.
.TP
.BI rate_iops_min \fR=\fPint
If this rate of I/O is not met, the job will exit. The same format as \fBrate\fR
is used for read vs write separation.
.TP
.BI rate_process \fR=\fPstr
This option controls how fio manages rated IO submissions. The default is
\fBlinear\fR, which submits IO in a linear fashion with fixed delays between
IOs that gets adjusted based on IO completion rates. If this is set to
\fBpoisson\fR, fio will submit IO based on a more real world random request
flow, known as the Poisson process
(https://en.wikipedia.org/wiki/Poisson_process). The lambda will be
10^6 / IOPS for the given workload.
.TP
.BI rate_cycle \fR=\fPint
Average bandwidth for \fBrate\fR and \fBrate_min\fR over this number of
milliseconds.  Default: 1000ms.
.TP
.BI latency_target \fR=\fPint
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. The
values is given in microseconds. See \fBlatency_window\fR and
\fBlatency_percentile\fR.
.TP
.BI latency_window \fR=\fPint
Used with \fBlatency_target\fR to specify the sample window that the job
is run at varying queue depths to test the performance. The value is given
in microseconds.
.TP
.BI latency_percentile \fR=\fPfloat
The percentage of IOs that must fall within the criteria specified by
\fBlatency_target\fR and \fBlatency_window\fR. If not set, this defaults
to 100.0, meaning that all IOs must be equal or below to the value set
by \fBlatency_target\fR.
.TP
.BI max_latency \fR=\fPint
If set, fio will exit the job if it exceeds this maximum latency. It will exit
with an ETIME error.
.TP
.BI cpumask \fR=\fPint
Set CPU affinity for this job. \fIint\fR is a bitmask of allowed CPUs the job
may run on.  See \fBsched_setaffinity\fR\|(2).
.TP
.BI cpus_allowed \fR=\fPstr
Same as \fBcpumask\fR, but allows a comma-delimited list of CPU numbers.
.TP
.BI cpus_allowed_policy \fR=\fPstr
Set the policy of how fio distributes the CPUs specified by \fBcpus_allowed\fR
or \fBcpumask\fR. Two policies are supported:
.RS
.RS
.TP
.B shared
All jobs will share the CPU set specified.
.TP
.B split
Each job will get a unique CPU from the CPU set.
.RE
.P
\fBshared\fR is the default behaviour, if the option isn't specified. If
\fBsplit\fR is specified, then fio will assign one cpu per job. If not enough
CPUs are given for the jobs listed, then fio will roundrobin the CPUs in
the set.
.RE
.P
.TP
.BI numa_cpu_nodes \fR=\fPstr
Set this job running on specified NUMA nodes' CPUs. The arguments allow
comma delimited list of cpu numbers, A-B ranges, or 'all'.
.TP
.BI numa_mem_policy \fR=\fPstr
Set this job's memory policy and corresponding NUMA nodes. Format of
the arguments:
.RS
.TP
.B <mode>[:<nodelist>]
.TP
.B mode
is one of the following memory policy:
.TP
.B default, prefer, bind, interleave, local
.TP
.RE
For \fBdefault\fR and \fBlocal\fR memory policy, no \fBnodelist\fR is
needed to be specified. For \fBprefer\fR, only one node is
allowed. For \fBbind\fR and \fBinterleave\fR, \fBnodelist\fR allows
comma delimited list of numbers, A-B ranges, or 'all'.
.TP
.BI startdelay \fR=\fPirange
Delay start of job for the specified number of seconds. Supports all time
suffixes to allow specification of hours, minutes, seconds and
milliseconds - seconds are the default if a unit is omitted.
Can be given as a range which causes each thread to choose randomly out of the
range.
.TP
.BI runtime \fR=\fPint
Terminate processing after the specified number of seconds.
.TP
.B time_based
If given, run for the specified \fBruntime\fR duration even if the files are
completely read or written. The same workload will be repeated as many times
as \fBruntime\fR allows.
.TP
.BI ramp_time \fR=\fPint
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 \fBramp_time\fR is considered lead in time for a job, thus it will
increase the total runtime if a special timeout or runtime is specified.
.TP
.BI invalidate \fR=\fPbool
Invalidate buffer-cache for the file prior to starting I/O.  Default: true.
.TP
.BI sync \fR=\fPbool
Use synchronous I/O for buffered writes.  For the majority of I/O engines,
this means using O_SYNC.  Default: false.
.TP
.BI iomem \fR=\fPstr "\fR,\fP mem" \fR=\fPstr
Allocation method for I/O unit buffer.  Allowed values are:
.RS
.RS
.TP
.B malloc
Allocate memory with \fBmalloc\fR\|(3).
.TP
.B shm
Use shared memory buffers allocated through \fBshmget\fR\|(2).
.TP
.B shmhuge
Same as \fBshm\fR, but use huge pages as backing.
.TP
.B mmap
Use \fBmmap\fR\|(2) for allocation.  Uses anonymous memory unless a filename
is given after the option in the format `:\fIfile\fR'.
.TP
.B mmaphuge
Same as \fBmmap\fR, but use huge files as backing.
.TP
.B mmapshared
Same as \fBmmap\fR, but use a MMAP_SHARED mapping.
.RE
.P
The amount of memory allocated is the maximum allowed \fBblocksize\fR for the
job multiplied by \fBiodepth\fR.  For \fBshmhuge\fR or \fBmmaphuge\fR to work,
the system must have free huge pages allocated.  \fBmmaphuge\fR also needs to
have hugetlbfs mounted, and \fIfile\fR must point there. At least on Linux,
huge pages must be manually allocated. See \fB/proc/sys/vm/nr_hugehages\fR
and the documentation for that. Normally you just need to echo an appropriate
number, eg echoing 8 will ensure that the OS has 8 huge pages ready for
use.
.RE
.TP
.BI iomem_align \fR=\fPint "\fR,\fP mem_align" \fR=\fPint
This indicates the memory alignment of the IO memory buffers. Note that the
given alignment is applied to the first IO unit buffer, if using \fBiodepth\fR
the alignment of the following buffers are given by the \fBbs\fR used. In
other words, if using a \fBbs\fR that is a multiple of the page sized in the
system, all buffers will be aligned to this value. If using a \fBbs\fR that
is not page aligned, the alignment of subsequent IO memory buffers is the
sum of the \fBiomem_align\fR and \fBbs\fR used.
.TP
.BI hugepage\-size \fR=\fPint
Defines the size of a huge page.  Must be at least equal to the system setting.
Should be a multiple of 1MB. Default: 4MB.
.TP
.B exitall
Terminate all jobs when one finishes.  Default: wait for each job to finish.
.TP
.B exitall_on_error \fR=\fPbool
Terminate all jobs if one job finishes in error.  Default: wait for each job
to finish.
.TP
.BI bwavgtime \fR=\fPint
Average bandwidth calculations over the given time in milliseconds.  Default:
500ms.
.TP
.BI iopsavgtime \fR=\fPint
Average IOPS calculations over the given time in milliseconds.  Default:
500ms.
.TP
.BI create_serialize \fR=\fPbool
If true, serialize file creation for the jobs.  Default: true.
.TP
.BI create_fsync \fR=\fPbool
\fBfsync\fR\|(2) data file after creation.  Default: true.
.TP
.BI create_on_open \fR=\fPbool
If true, the files are not created until they are opened for IO by the job.
.TP
.BI create_only \fR=\fPbool
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.
.TP
.BI allow_file_create \fR=\fPbool
If true, fio is permitted to create files as part of its workload. This is
the default behavior. If this option is false, then fio will error out if the
files it needs to use don't already exist. Default: true.
.TP
.BI allow_mounted_write \fR=\fPbool
If this isn't set, fio will abort jobs that are destructive (eg 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. Default: false.
.TP
.BI pre_read \fR=\fPbool
If this is given, files will be pre-read into memory before starting the given
IO operation. This will also clear the \fR \fBinvalidate\fR flag, since it is
pointless to pre-read and then drop the cache. This will only work for IO
engines that are seekable, since they allow you to read the same data
multiple times. Thus it will not work on eg network or splice IO.
.TP
.BI unlink \fR=\fPbool
Unlink job files when done.  Default: false.
.TP
.BI loops \fR=\fPint
Specifies the number of iterations (runs of the same workload) of this job.
Default: 1.
.TP
.BI verify_only \fR=\fPbool
Do not perform the 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
\fBtime_based\fR option set.
.TP
.BI do_verify \fR=\fPbool
Run the verify phase after a write phase.  Only valid if \fBverify\fR is set.
Default: true.
.TP
.BI verify \fR=\fPstr
Method of verifying 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.  \fBverify\fR=str can be combined with \fBverify_pattern\fR=str
option.  The allowed values are:
.RS
.RS
.TP
.B md5 crc16 crc32 crc32c crc32c-intel crc64 crc7 sha256 sha512 sha1 xxhash
Store appropriate checksum in the header of each block. crc32c-intel is
hardware accelerated SSE4.2 driven, falls back to regular crc32c if
not supported by the system.
.TP
.B 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 \fBverify\fR=str setting. This option
is kept because of compatibility's sake with old configurations. Do not use it.
.TP
.B 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 \fBverify_pattern\fR is verified.
.TP
.B null
Pretend to verify.  Used for testing internals.
.RE

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.
.RE
.TP
.BI verifysort \fR=\fPbool
If true, written verify blocks are sorted if \fBfio\fR deems it to be faster to
read them back in a sorted manner.  Default: true.
.TP
.BI verifysort_nr \fR=\fPint
Pre-load and sort verify blocks for a read workload.
.TP
.BI verify_offset \fR=\fPint
Swap the verification header with data somewhere else in the block before
writing.  It is swapped back before verifying.
.TP
.BI verify_interval \fR=\fPint
Write the verification header for this number of bytes, which should divide
\fBblocksize\fR.  Default: \fBblocksize\fR.
.TP
.BI verify_pattern \fR=\fPstr
If set, fio will fill the io buffers with this pattern. Fio defaults to filling
with totally random bytes, but sometimes it's interesting to fill with a known
pattern for io 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
\fBverify\fP=str. Also, verify_pattern supports %o format, which means that for
each block offset will be written and then verifyied back, e.g.:
.RS
.RS
\fBverify_pattern\fR=%o
.RE
Or use combination of everything:
.LP
.RS
\fBverify_pattern\fR=0xff%o"abcd"-21
.RE
.RE
.TP
.BI verify_fatal \fR=\fPbool
If true, exit the job on the first observed verification failure.  Default:
false.
.TP
.BI verify_dump \fR=\fPbool
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.
.TP
.BI verify_async \fR=\fPint
Fio will normally verify IO inline from the submitting thread. This option
takes an integer describing how many async offload threads to create for IO
verification instead, causing fio to offload the duty of verifying IO contents
to one or more separate threads.  If using this offload option, even sync IO
engines can benefit from using an \fBiodepth\fR setting higher than 1, as it
allows them to have IO in flight while verifies are running.
.TP
.BI verify_async_cpus \fR=\fPstr
Tell fio to set the given CPU affinity on the async IO verification threads.
See \fBcpus_allowed\fP for the format used.
.TP
.BI verify_backlog \fR=\fPint
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
IO 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.
.TP
.BI verify_backlog_batch \fR=\fPint
Control how many blocks fio will verify if verify_backlog is set. If not set,
will default to the value of \fBverify_backlog\fR (meaning the entire queue is
read back and verified).  If \fBverify_backlog_batch\fR is less than
\fBverify_backlog\fR then not all blocks will be verified,  if
\fBverify_backlog_batch\fR is larger than \fBverify_backlog\fR,  some blocks
will be verified more than once.
.TP
.BI trim_percentage \fR=\fPint
Number of verify blocks to discard/trim.
.TP
.BI trim_verify_zero \fR=\fPbool
Verify that trim/discarded blocks are returned as zeroes.
.TP
.BI trim_backlog \fR=\fPint
Trim after this number of blocks are written.
.TP
.BI trim_backlog_batch \fR=\fPint
Trim this number of IO blocks.
.TP
.BI experimental_verify \fR=\fPbool
Enable experimental verification.
.TP
.BI verify_state_save \fR=\fPbool
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.
.TP
.BI verify_state_load \fR=\fPbool
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.
.TP
.B stonewall "\fR,\fP wait_for_previous"
Wait for preceding jobs in the job file to exit before starting this one.
\fBstonewall\fR implies \fBnew_group\fR.
.TP
.B new_group
Start a new reporting group.  If not given, all jobs in a file will be part
of the same reporting group, unless separated by a stonewall.
.TP
.BI numjobs \fR=\fPint
Number of clones (processes/threads performing the same workload) of this job.
Default: 1.
.TP
.B group_reporting
If set, display per-group reports instead of per-job when \fBnumjobs\fR is
specified.
.TP
.B thread
Use threads created with \fBpthread_create\fR\|(3) instead of processes created
with \fBfork\fR\|(2).
.TP
.BI zonesize \fR=\fPint
Divide file into zones of the specified size in bytes.  See \fBzoneskip\fR.
.TP
.BI zonerange \fR=\fPint
Give size of an IO zone.  See \fBzoneskip\fR.
.TP
.BI zoneskip \fR=\fPint
Skip the specified number of bytes when \fBzonesize\fR bytes of data have been
read.
.TP
.BI write_iolog \fR=\fPstr
Write the issued I/O patterns to the specified file.  Specify a separate file
for each job, otherwise the iologs will be interspersed and the file may be
corrupt.
.TP
.BI read_iolog \fR=\fPstr
Replay the I/O patterns contained in the specified file generated by
\fBwrite_iolog\fR, or may be a \fBblktrace\fR binary file.
.TP
.BI replay_no_stall \fR=\fPint
While replaying I/O patterns using \fBread_iolog\fR the default behavior
attempts to respect timing information between I/Os.  Enabling
\fBreplay_no_stall\fR causes I/Os to be replayed as fast as possible while
still respecting ordering.
.TP
.BI replay_redirect \fR=\fPstr
While replaying I/O patterns using \fBread_iolog\fR the default behavior
is to replay the IOPS onto the major/minor device that each IOP was recorded
from.  Setting \fBreplay_redirect\fR causes all IOPS to be replayed onto the
single specified device regardless of the device it was recorded from.
.TP
.BI replay_align \fR=\fPint
Force alignment of IO offsets and lengths in a trace to this power of 2 value.
.TP
.BI replay_scale \fR=\fPint
Scale sector offsets down by this factor when replaying traces.
.TP
.BI per_job_logs \fR=\fPbool
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.
.TP
.BI write_bw_log \fR=\fPstr
If given, write a bandwidth log of the jobs in this job file. Can be used to
store data of the bandwidth of the jobs in their lifetime. The included
fio_generate_plots script uses gnuplot to turn these text files into nice
graphs. See \fBwrite_lat_log\fR for behaviour of given filename. For this
option, the postfix is _bw.x.log, where x is the index of the job (1..N,
where N is the number of jobs). If \fBper_job_logs\fR is false, then the
filename will not include the job index.
.TP
.BI write_lat_log \fR=\fPstr
Same as \fBwrite_bw_log\fR, but writes I/O completion latencies.  If no
filename is given with this option, the default filename of
"jobname_type.x.log" is used, where x is the index of the job (1..N, where
N is the number of jobs). Even if the filename is given, fio will still
append the type of log. If \fBper_job_logs\fR is false, then the filename will
not include the job index.
.TP
.BI write_iops_log \fR=\fPstr
Same as \fBwrite_bw_log\fR, but writes IOPS. If no filename is given with this
option, the default filename of "jobname_type.x.log" is used, where x is the
index of the job (1..N, where N is the number of jobs). Even if the filename
is given, fio will still append the type of log. If \fBper_job_logs\fR is false,
then the filename will not include the job index.
.TP
.BI log_avg_msec \fR=\fPint
By default, fio will log an entry in the iops, latency, or bw log for every
IO 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
\fBlog_max\fR as well.  Defaults to 0, logging all entries.
.TP
.BI log_max \fR=\fPbool
If \fBlog_avg_msec\fR 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.
.TP
.BI log_offset \fR=\fPbool
If this is set, the iolog options will include the byte offset for the IO
entry as well as the other data values.
.TP
.BI log_compression \fR=\fPint
If this is set, fio will compress the IO 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 IO 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 IO 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.
.TP
.BI log_compression_cpus \fR=\fPstr
Define the set of CPUs that are allowed to handle online log compression
for the IO jobs. This can provide better isolation between performance
sensitive jobs, and background compression work.
.TP
.BI log_store_compressed \fR=\fPbool
If set, fio will store the log files in a compressed format. They can be
decompressed with fio, using the \fB\-\-inflate-log\fR command line parameter.
The files will be stored with a \fB\.fz\fR suffix.
.TP
.BI block_error_percentiles \fR=\fPbool
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.
.TP
.BI disable_lat \fR=\fPbool
Disable measurements of total latency numbers. Useful only for cutting
back the number of calls to \fBgettimeofday\fR\|(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 disable_slat and disable_bw as well.
.TP
.BI disable_clat \fR=\fPbool
Disable measurements of completion latency numbers. See \fBdisable_lat\fR.
.TP
.BI disable_slat \fR=\fPbool
Disable measurements of submission latency numbers. See \fBdisable_lat\fR.
.TP
.BI disable_bw_measurement \fR=\fPbool
Disable measurements of throughput/bandwidth numbers. See \fBdisable_lat\fR.
.TP
.BI lockmem \fR=\fPint
Pin the specified amount of memory with \fBmlock\fR\|(2).  Can be used to
simulate a smaller amount of memory. The amount specified is per worker.
.TP
.BI exec_prerun \fR=\fPstr
Before running the job, execute the specified command with \fBsystem\fR\|(3).
.RS
Output is redirected in a file called \fBjobname.prerun.txt\fR
.RE
.TP
.BI exec_postrun \fR=\fPstr
Same as \fBexec_prerun\fR, but the command is executed after the job completes.
.RS
Output is redirected in a file called \fBjobname.postrun.txt\fR
.RE
.TP
.BI ioscheduler \fR=\fPstr
Attempt to switch the device hosting the file to the specified I/O scheduler.
.TP
.BI disk_util \fR=\fPbool
Generate disk utilization statistics if the platform supports it. Default: true.
.TP
.BI clocksource \fR=\fPstr
Use the given clocksource as the base of timing. The supported options are:
.RS
.TP
.B gettimeofday
\fBgettimeofday\fR\|(2)
.TP
.B clock_gettime
\fBclock_gettime\fR\|(2)
.TP
.B cpu
Internal CPU clock source
.TP
.RE
.P
\fBcpu\fR 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.
.TP
.BI gtod_reduce \fR=\fPbool
Enable all of the \fBgettimeofday\fR\|(2) reducing options (disable_clat, disable_slat,
disable_bw) plus reduce precision of the timeout somewhat to really shrink the
\fBgettimeofday\fR\|(2) call count. With this option enabled, we only do about 0.4% of
the gtod() calls we would have done if all time keeping was enabled.
.TP
.BI gtod_cpu \fR=\fPint
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
\fBgettimeofday\fR\|(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 IO workloads need only copy that segment, instead of
entering the kernel with a \fBgettimeofday\fR\|(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.
.TP
.BI ignore_error \fR=\fPstr
Sometimes you want to ignore some errors during test in that case you can specify
error list for each error type.
.br
ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST
.br
errors for given error type is separated with ':'.
Error may be symbol ('ENOSPC', 'ENOMEM') or an integer.
.br
Example: ignore_error=EAGAIN,ENOSPC:122 .
.br
This option will ignore EAGAIN from READ, and ENOSPC and 122(EDQUOT) from WRITE.
.TP
.BI error_dump \fR=\fPbool
If set dump every error even if it is non fatal, true by default. If disabled
only fatal error will be dumped
.TP
.BI profile \fR=\fPstr
Select a specific builtin performance test.
.TP
.BI cgroup \fR=\fPstr
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
.TP
.BI cgroup_weight \fR=\fPint
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.
.TP
.BI cgroup_nodelete \fR=\fPbool
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
.TP
.BI uid \fR=\fPint
Instead of running as the invoking user, set the user ID to this value before
the thread/process does any work.
.TP
.BI gid \fR=\fPint
Set group ID, see \fBuid\fR.
.TP
.BI unit_base \fR=\fPint
Base unit for reporting.  Allowed values are:
.RS
.TP
.B 0
Use auto-detection (default).
.TP
.B 8
Byte based.
.TP
.B 1
Bit based.
.RE
.P
.TP
.BI flow_id \fR=\fPint
The ID of the flow. If not specified, it defaults to being a global flow. See
\fBflow\fR.
.TP
.BI flow \fR=\fPint
Weight in token-based flow control. If this value is used, then there is a
\fBflow counter\fR which is used to regulate the proportion of activity between
two or more jobs. fio attempts to keep this flow counter near zero. The
\fBflow\fR 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
\fBflow=8\fR and another job has \fBflow=-1\fR, then there will be a roughly
1:8 ratio in how much one runs vs the other.
.TP
.BI flow_watermark \fR=\fPint
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.
.TP
.BI flow_sleep \fR=\fPint
The period of time, in microseconds, to wait after the flow watermark has been
exceeded before retrying operations
.TP
.BI clat_percentiles \fR=\fPbool
Enable the reporting of percentiles of completion latencies.
.TP
.BI percentile_list \fR=\fPfloat_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. 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.
.SS "Ioengine Parameters List"
Some parameters are only valid when a specific 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 ioengine.
.TP
.BI (cpu)cpuload \fR=\fPint
Attempt to use the specified percentage of CPU cycles.
.TP
.BI (cpu)cpuchunks \fR=\fPint
Split the load into cycles of the given time. In microseconds.
.TP
.BI (cpu)exit_on_io_done \fR=\fPbool
Detect when IO threads are done, then exit.
.TP
.BI (libaio)userspace_reap
Normally, with the libaio engine in use, fio will use
the io_getevents 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 (eg when
iodepth_batch_complete=0).
.TP
.BI (psyncv2)hipri
Set RWF_HIPRI on IO, indicating to the kernel that it's of
higher priority than normal.
.TP
.BI (net,netsplice)hostname \fR=\fPstr
The host name or IP address to use for TCP or UDP based IO.
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.
.TP
.BI (net,netsplice)port \fR=\fPint
The TCP or UDP port to bind to or connect to. If this is used with
\fBnumjobs\fR 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.
.TP
.BI (net,netsplice)interface \fR=\fPstr
The IP address of the network interface used to send or receive UDP multicast
packets.
.TP
.BI (net,netsplice)ttl \fR=\fPint
Time-to-live value for outgoing UDP multicast packets. Default: 1
.TP
.BI (net,netsplice)nodelay \fR=\fPbool
Set TCP_NODELAY on TCP connections.
.TP
.BI (net,netsplice)protocol \fR=\fPstr "\fR,\fP proto" \fR=\fPstr
The network protocol to use. Accepted values are:
.RS
.RS
.TP
.B tcp
Transmission control protocol
.TP
.B tcpv6
Transmission control protocol V6
.TP
.B udp
User datagram protocol
.TP
.B udpv6
User datagram protocol V6
.TP
.B unix
UNIX domain socket
.RE
.P
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 filename option should be
used and the port is invalid.
.RE
.TP
.BI (net,netsplice)listen
For TCP network connections, tell fio to listen for incoming
connections rather than initiating an outgoing connection. The
hostname must be omitted if this option is used.
.TP
.BI (net, pingpong) \fR=\fPbool
Normally a network writer will just continue writing data, and a network reader
will just consume packets. 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.
.TP
.BI (net, window_size) \fR=\fPint
Set the desired socket buffer size for the connection.
.TP
.BI (net, mss) \fR=\fPint
Set the TCP maximum segment size (TCP_MAXSEG).
.TP
.BI (e4defrag,donorname) \fR=\fPstr
File will be used as a block donor (swap extents between files)
.TP
.BI (e4defrag,inplace) \fR=\fPint
Configure donor file block allocation strategy
.RS
.BI 0(default) :
Preallocate donor's file on init
.TP
.BI 1:
allocate space immediately inside defragment event, and free right after event
.RE
.TP
.BI (rbd)rbdname \fR=\fPstr
Specifies the name of the RBD.
.TP
.BI (rbd)pool \fR=\fPstr
Specifies the name of the Ceph pool containing the RBD.
.TP
.BI (rbd)clientname \fR=\fPstr
Specifies the username (without the 'client.' prefix) used to access the Ceph cluster.
.TP
.BI (mtd)skipbad \fR=\fPbool
Skip operations against known bad blocks.
.SH OUTPUT
While running, \fBfio\fR will display the status of the created jobs.  For
example:
.RS
.P
Threads: 1: [_r] [24.8% done] [ 13509/  8334 kb/s] [eta 00h:01m:31s]
.RE
.P
The characters in the first set of brackets denote the current status of each
threads.  The possible values are:
.P
.PD 0
.RS
.TP
.B P
Setup but not started.
.TP
.B C
Thread created.
.TP
.B I
Initialized, waiting.
.TP
.B R
Running, doing sequential reads.
.TP
.B r
Running, doing random reads.
.TP
.B W
Running, doing sequential writes.
.TP
.B w
Running, doing random writes.
.TP
.B M
Running, doing mixed sequential reads/writes.
.TP
.B m
Running, doing mixed random reads/writes.
.TP
.B F
Running, currently waiting for \fBfsync\fR\|(2).
.TP
.B V
Running, verifying written data.
.TP
.B E
Exited, not reaped by main thread.
.TP
.B \-
Exited, thread reaped.
.RE
.PD
.P
The second set of brackets shows the estimated completion percentage of
the current group.  The third set shows the read and write I/O rate,
respectively. Finally, the estimated run time of the job is displayed.
.P
When \fBfio\fR completes (or is interrupted by Ctrl-C), it will show data
for each thread, each group of threads, and each disk, in that order.
.P
Per-thread statistics first show the threads client number, group-id, and
error code.  The remaining figures are as follows:
.RS
.TP
.B io
Number of megabytes of I/O performed.
.TP
.B bw
Average data rate (bandwidth).
.TP
.B runt
Threads run time.
.TP
.B slat
Submission latency minimum, maximum, average and standard deviation. This is
the time it took to submit the I/O.
.TP
.B clat
Completion latency minimum, maximum, average and standard deviation.  This
is the time between submission and completion.
.TP
.B bw
Bandwidth minimum, maximum, percentage of aggregate bandwidth received, average
and standard deviation.
.TP
.B cpu
CPU usage statistics. Includes user and system time, number of context switches
this thread went through and number of major and minor page faults.
.TP
.B IO depths
Distribution of I/O depths.  Each depth includes everything less than (or equal)
to it, but greater than the previous depth.
.TP
.B IO issued
Number of read/write requests issued, and number of short read/write requests.
.TP
.B IO latencies
Distribution of I/O completion latencies.  The numbers follow the same pattern
as \fBIO depths\fR.
.RE
.P
The group statistics show:
.PD 0
.RS
.TP
.B io
Number of megabytes I/O performed.
.TP
.B aggrb
Aggregate bandwidth of threads in the group.
.TP
.B minb
Minimum average bandwidth a thread saw.
.TP
.B maxb
Maximum average bandwidth a thread saw.
.TP
.B mint
Shortest runtime of threads in the group.
.TP
.B maxt
Longest runtime of threads in the group.
.RE
.PD
.P
Finally, disk statistics are printed with reads first:
.PD 0
.RS
.TP
.B ios
Number of I/Os performed by all groups.
.TP
.B merge
Number of merges in the I/O scheduler.
.TP
.B ticks
Number of ticks we kept the disk busy.
.TP
.B io_queue
Total time spent in the disk queue.
.TP
.B util
Disk utilization.
.RE
.PD
.P
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 \fBUSR1\fR
signal.
.SH TERSE OUTPUT
If the \fB\-\-minimal\fR / \fB\-\-append-terse\fR options are given, the
results will be printed/appended in a semicolon-delimited format suitable for
scripted use.
A job description (if provided) follows on a new line.  Note that the first
number in the line is the version number. If the output has to be changed
for some reason, this number will be incremented by 1 to signify that
change.  The fields are:
.P
.RS
.B terse version, fio version, jobname, groupid, error
.P
Read status:
.RS
.B Total I/O \fR(KB)\fP, bandwidth \fR(KB/s)\fP, IOPS, runtime \fR(ms)\fP
.P
Submission latency:
.RS
.B min, max, mean, standard deviation
.RE
Completion latency:
.RS
.B min, max, mean, standard deviation
.RE
Completion latency percentiles (20 fields):
.RS
.B Xth percentile=usec
.RE
Total latency:
.RS
.B min, max, mean, standard deviation
.RE
Bandwidth:
.RS
.B min, max, aggregate percentage of total, mean, standard deviation
.RE
.RE
.P
Write status:
.RS
.B Total I/O \fR(KB)\fP, bandwidth \fR(KB/s)\fP, IOPS, runtime \fR(ms)\fP
.P
Submission latency:
.RS
.B min, max, mean, standard deviation
.RE
Completion latency:
.RS
.B min, max, mean, standard deviation
.RE
Completion latency percentiles (20 fields):
.RS
.B Xth percentile=usec
.RE
Total latency:
.RS
.B min, max, mean, standard deviation
.RE
Bandwidth:
.RS
.B min, max, aggregate percentage of total, mean, standard deviation
.RE
.RE
.P
CPU usage:
.RS
.B user, system, context switches, major page faults, minor page faults
.RE
.P
IO depth distribution:
.RS
.B <=1, 2, 4, 8, 16, 32, >=64
.RE
.P
IO latency distribution:
.RS
Microseconds:
.RS
.B <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000
.RE
Milliseconds:
.RS
.B <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, 2000, >=2000
.RE
.RE
.P
Disk utilization (1 for each disk used):
.RS
.B name, read ios, write ios, read merges, write merges, read ticks, write ticks, read in-queue time, write in-queue time, disk utilization percentage
.RE
.P
Error Info (dependent on continue_on_error, default off):
.RS
.B total # errors, first error code
.RE
.P
.B text description (if provided in config - appears on newline)
.RE
.SH 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.

.P
.B Trace file format v1
.RS
Each line represents a single io 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.

.RE
.P
.B Trace file format v2
.RS
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:

\fBfio version 2 iolog\fR

Following this can be lines in two different formats, which are described below.
The file management format:

\fBfilename action\fR

The filename is given as an absolute path. The action can be one of these:

.P
.PD 0
.RS
.TP
.B add
Add the given filename to the trace
.TP
.B open
Open the file with the given filename. The filename has to have been previously
added with the \fBadd\fR action.
.TP
.B close
Close the file with the given filename. The file must have previously been
opened.
.RE
.PD
.P

The file io action format:

\fBfilename action offset length\fR

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:

.P
.PD 0
.RS
.TP
.B wait
Wait for 'offset' microseconds. Everything below 100 is discarded.  The time is
relative to the previous wait statement.
.TP
.B read
Read \fBlength\fR bytes beginning from \fBoffset\fR
.TP
.B write
Write \fBlength\fR bytes beginning from \fBoffset\fR
.TP
.B sync
fsync() the file
.TP
.B datasync
fdatasync() the file
.TP
.B trim
trim the given file from the given \fBoffset\fR for \fBlength\fR bytes
.RE
.PD
.P

.SH 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.

.SH 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 IO 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:

.RS
Storing the write state of each job
.LP
Executing a trigger command
.RE

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 (\fBtouch\fR) of a specified
file in the system, or through a timeout setting. If fio is run with
\fB\-\-trigger\-file=/tmp/trigger-file\fR, then it will continually check for
the existence of /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.

.RE
.P
.B Verification trigger example
.RS

Lets say we want to run a powercut test on the remote machine 'server'.
Our write workload is in 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# \fBfio \-\-server\fR

and on the client, we'll fire off the workload:

localbox$ \fBfio \-\-client=server \-\-trigger\-file=/tmp/my\-trigger \-\-trigger-remote="bash \-c "echo b > /proc/sysrq-triger""\fR

We set \fB/tmp/my-trigger\fR as the trigger file, and we tell fio to execute

\fBecho b > /proc/sysrq-trigger\fR

on the server once it has received the trigger and sent us the write
state. This will work, but it's not \fIreally\fR 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. Lets 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$ \fBfio \-\-client=server \-\-trigger\-file=/tmp/my\-trigger \-\-trigger="ipmi-reboot server"\fR

For this case, fio would wait for the server to send us the write state,
then execute 'ipmi-reboot server' when that happened.

.RE
.P
.B Loading verify state
.RS
To load store write state, read verification job file must contain
the 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.

.RE

.SH CLIENT / SERVER
Normally you would run fio as a stand-alone application on the machine
where the IO workload should be generated. However, it is also possible to
run the frontend and backend of fio separately. This makes it possible to
have a fio server running on the machine(s) where the IO workload should
be running, while controlling it from another machine.

To start the server, you would do:

\fBfio \-\-server=args\fR

on that machine, 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) \fBfio \-\-server\fR

   Start a fio server, listening on all interfaces on the default port (8765).

2) \fBfio \-\-server=ip:hostname,4444\fR

   Start a fio server, listening on IP belonging to hostname and on port 4444.

3) \fBfio \-\-server=ip6:::1,4444\fR

   Start a fio server, listening on IPv6 localhost ::1 and on port 4444.

4) \fBfio \-\-server=,4444\fR

   Start a fio server, listening on all interfaces on port 4444.

5) \fBfio \-\-server=1.2.3.4\fR

   Start a fio server, listening on IP 1.2.3.4 on the default port.

6) \fBfio \-\-server=sock:/tmp/fio.sock\fR

   Start a fio server, listening on the local socket /tmp/fio.sock.

When a server is running, you can connect to it from a client. The client
is run with:

\fBfio \-\-local-args \-\-client=server \-\-remote-args <job file(s)>\fR

where \-\-local-args are arguments that are local to 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.
You can connect to multiple clients as well, to do that you could run:

\fBfio \-\-client=server2 \-\-client=server2 <job file(s)>\fR

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 \-\-remote-config:

\fBfio \-\-client=server \-\-remote-config /path/to/file.fio\fR

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 \-\-client option.
For example, here is an example "host.list" file containing 2 hostnames:

host1.your.dns.domain
.br
host2.your.dns.domain

The fio command would then be:

\fBfio \-\-client=host.list <job file>\fR

In this mode, you cannot input server-specific parameters or job files, and all
servers receive the same job file.

In order to enable fio \-\-client runs utilizing 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 directory /mnt/nfs/fio and is writing filename fileio.tmp,
with a \-\-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
.br
/mnt/nfs/fio/192.168.10.121.fileio.tmp

.SH AUTHORS

.B fio
was written by Jens Axboe <jens.axboe@oracle.com>,
now Jens Axboe <axboe@fb.com>.
.br
This man page was written by Aaron Carroll <aaronc@cse.unsw.edu.au> based
on documentation by Jens Axboe.
.SH "REPORTING BUGS"
Report bugs to the \fBfio\fR mailing list <fio@vger.kernel.org>.
See \fBREADME\fR.
.SH "SEE ALSO"
For further documentation see \fBHOWTO\fR and \fBREADME\fR.
.br
Sample jobfiles are available in the \fBexamples\fR directory.