8 5. Detailed list of parameters
12 9. CPU idleness profiling
14 1.0 Overview and history
15 ------------------------
16 fio was originally written to save me the hassle of writing special test
17 case programs when I wanted to test a specific workload, either for
18 performance reasons or to find/reproduce a bug. The process of writing
19 such a test app can be tiresome, especially if you have to do it often.
20 Hence I needed a tool that would be able to simulate a given io workload
21 without resorting to writing a tailored test case again and again.
23 A test work load is difficult to define, though. There can be any number
24 of processes or threads involved, and they can each be using their own
25 way of generating io. You could have someone dirtying large amounts of
26 memory in an memory mapped file, or maybe several threads issuing
27 reads using asynchronous io. fio needed to be flexible enough to
28 simulate both of these cases, and many more.
32 The first step in getting fio to simulate a desired io workload, is
33 writing a job file describing that specific setup. A job file may contain
34 any number of threads and/or files - the typical contents of the job file
35 is a global section defining shared parameters, and one or more job
36 sections describing the jobs involved. When run, fio parses this file
37 and sets everything up as described. If we break down a job from top to
38 bottom, it contains the following basic parameters:
40 IO type Defines the io pattern issued to the file(s).
41 We may only be reading sequentially from this
42 file(s), or we may be writing randomly. Or even
43 mixing reads and writes, sequentially or randomly.
45 Block size In how large chunks are we issuing io? This may be
46 a single value, or it may describe a range of
49 IO size How much data are we going to be reading/writing.
51 IO engine How do we issue io? We could be memory mapping the
52 file, we could be using regular read/write, we
53 could be using splice, async io, syslet, or even
56 IO depth If the io engine is async, how large a queuing
57 depth do we want to maintain?
59 IO type Should we be doing buffered io, or direct/raw io?
61 Num files How many files are we spreading the workload over.
63 Num threads How many threads or processes should we spread
66 The above are the basic parameters defined for a workload, in addition
67 there's a multitude of parameters that modify other aspects of how this
73 See the README file for command line parameters, there are only a few
76 Running fio is normally the easiest part - you just give it the job file
77 (or job files) as parameters:
81 and it will start doing what the job_file tells it to do. You can give
82 more than one job file on the command line, fio will serialize the running
83 of those files. Internally that is the same as using the 'stonewall'
84 parameter described in the parameter section.
86 If the job file contains only one job, you may as well just give the
87 parameters on the command line. The command line parameters are identical
88 to the job parameters, with a few extra that control global parameters
89 (see README). For example, for the job file parameter iodepth=2, the
90 mirror command line option would be --iodepth 2 or --iodepth=2. You can
91 also use the command line for giving more than one job entry. For each
92 --name option that fio sees, it will start a new job with that name.
93 Command line entries following a --name entry will apply to that job,
94 until there are no more entries or a new --name entry is seen. This is
95 similar to the job file options, where each option applies to the current
96 job until a new [] job entry is seen.
98 fio does not need to run as root, except if the files or devices specified
99 in the job section requires that. Some other options may also be restricted,
100 such as memory locking, io scheduler switching, and decreasing the nice value.
105 As previously described, fio accepts one or more job files describing
106 what it is supposed to do. The job file format is the classic ini file,
107 where the names enclosed in [] brackets define the job name. You are free
108 to use any ascii name you want, except 'global' which has special meaning.
109 A global section sets defaults for the jobs described in that file. A job
110 may override a global section parameter, and a job file may even have
111 several global sections if so desired. A job is only affected by a global
112 section residing above it. If the first character in a line is a ';' or a
113 '#', the entire line is discarded as a comment.
115 So let's look at a really simple job file that defines two processes, each
116 randomly reading from a 128MB file.
118 ; -- start job file --
129 As you can see, the job file sections themselves are empty as all the
130 described parameters are shared. As no filename= option is given, fio
131 makes up a filename for each of the jobs as it sees fit. On the command
132 line, this job would look as follows:
134 $ fio --name=global --rw=randread --size=128m --name=job1 --name=job2
137 Let's look at an example that has a number of processes writing randomly
140 ; -- start job file --
152 Here we have no global section, as we only have one job defined anyway.
153 We want to use async io here, with a depth of 4 for each file. We also
154 increased the buffer size used to 32KB and define numjobs to 4 to
155 fork 4 identical jobs. The result is 4 processes each randomly writing
156 to their own 64MB file. Instead of using the above job file, you could
157 have given the parameters on the command line. For this case, you would
160 $ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4
162 4.1 Environment variables
163 -------------------------
165 fio also supports environment variable expansion in job files. Any
166 substring of the form "${VARNAME}" as part of an option value (in other
167 words, on the right of the `='), will be expanded to the value of the
168 environment variable called VARNAME. If no such environment variable
169 is defined, or VARNAME is the empty string, the empty string will be
172 As an example, let's look at a sample fio invocation and job file:
174 $ SIZE=64m NUMJOBS=4 fio jobfile.fio
176 ; -- start job file --
183 This will expand to the following equivalent job file at runtime:
185 ; -- start job file --
192 fio ships with a few example job files, you can also look there for
195 4.2 Reserved keywords
196 ---------------------
198 Additionally, fio has a set of reserved keywords that will be replaced
199 internally with the appropriate value. Those keywords are:
201 $pagesize The architecture page size of the running system
202 $mb_memory Megabytes of total memory in the system
203 $ncpus Number of online available CPUs
205 These can be used on the command line or in the job file, and will be
206 automatically substituted with the current system values when the job
207 is run. Simple math is also supported on these keywords, so you can
208 perform actions like:
212 and get that properly expanded to 8 times the size of memory in the
216 5.0 Detailed list of parameters
217 -------------------------------
219 This section describes in details each parameter associated with a job.
220 Some parameters take an option of a given type, such as an integer or
221 a string. The following types are used:
223 str String. This is a sequence of alpha characters.
224 time Integer with possible time suffix. In seconds unless otherwise
225 specified, use eg 10m for 10 minutes. Accepts s/m/h for seconds,
226 minutes, and hours, and accepts 'ms' (or 'msec') for milliseconds,
227 and 'us' (or 'usec') for microseconds.
228 int SI integer. A whole number value, which may contain a suffix
229 describing the base of the number. Accepted suffixes are k/m/g/t/p,
230 meaning kilo, mega, giga, tera, and peta. The suffix is not case
231 sensitive, and you may also include trailing 'b' (eg 'kb' is the same
232 as 'k'). So if you want to specify 4096, you could either write
233 out '4096' or just give 4k. The suffixes signify base 2 values, so
234 1024 is 1k and 1024k is 1m and so on, unless the suffix is explicitly
235 set to a base 10 value using 'kib', 'mib', 'gib', etc. If that is the
236 case, then 1000 is used as the multiplier. This can be handy for
237 disks, since manufacturers generally use base 10 values when listing
238 the capacity of a drive. If the option accepts an upper and lower
239 range, use a colon ':' or minus '-' to separate such values. May also
240 include a prefix to indicate numbers base. If 0x is used, the number
241 is assumed to be hexadecimal. See irange.
242 bool Boolean. Usually parsed as an integer, however only defined for
243 true and false (1 and 0).
244 irange Integer range with suffix. Allows value range to be given, such
245 as 1024-4096. A colon may also be used as the separator, eg
246 1k:4k. If the option allows two sets of ranges, they can be
247 specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see
249 float_list A list of floating numbers, separated by a ':' character.
251 With the above in mind, here follows the complete list of fio job
254 name=str ASCII name of the job. This may be used to override the
255 name printed by fio for this job. Otherwise the job
256 name is used. On the command line this parameter has the
257 special purpose of also signaling the start of a new
260 description=str Text description of the job. Doesn't do anything except
261 dump this text description when this job is run. It's
264 directory=str Prefix filenames with this directory. Used to place files
265 in a different location than "./". See the 'filename' option
266 for escaping certain characters.
268 filename=str Fio normally makes up a filename based on the job name,
269 thread number, and file number. If you want to share
270 files between threads in a job or several jobs, specify
271 a filename for each of them to override the default. If
272 the ioengine used is 'net', the filename is the host, port,
273 and protocol to use in the format of =host,port,protocol.
274 See ioengine=net for more. If the ioengine is file based, you
275 can specify a number of files by separating the names with a
276 ':' colon. So if you wanted a job to open /dev/sda and /dev/sdb
277 as the two working files, you would use
278 filename=/dev/sda:/dev/sdb. On Windows, disk devices are
279 accessed as \\.\PhysicalDrive0 for the first device,
280 \\.\PhysicalDrive1 for the second etc. Note: Windows and
281 FreeBSD prevent write access to areas of the disk containing
282 in-use data (e.g. filesystems).
283 If the wanted filename does need to include a colon, then
284 escape that with a '\' character. For instance, if the filename
285 is "/dev/dsk/foo@3,0:c", then you would use
286 filename="/dev/dsk/foo@3,0\:c". '-' is a reserved name, meaning
287 stdin or stdout. Which of the two depends on the read/write
291 If sharing multiple files between jobs, it is usually necessary
292 to have fio generate the exact names that you want. By default,
293 fio will name a file based on the default file format
294 specification of jobname.jobnumber.filenumber. With this
295 option, that can be customized. Fio will recognize and replace
296 the following keywords in this string:
299 The name of the worker thread or process.
302 The incremental number of the worker thread or
306 The incremental number of the file for that worker
309 To have dependent jobs share a set of files, this option can
310 be set to have fio generate filenames that are shared between
311 the two. For instance, if testfiles.$filenum is specified,
312 file number 4 for any job will be named testfiles.4. The
313 default of $jobname.$jobnum.$filenum will be used if
314 no other format specifier is given.
316 opendir=str Tell fio to recursively add any file it can find in this
317 directory and down the file system tree.
319 lockfile=str Fio defaults to not locking any files before it does
320 IO to them. If a file or file descriptor is shared, fio
321 can serialize IO to that file to make the end result
322 consistent. This is usual for emulating real workloads that
323 share files. The lock modes are:
325 none No locking. The default.
326 exclusive Only one thread/process may do IO,
327 excluding all others.
328 readwrite Read-write locking on the file. Many
329 readers may access the file at the
330 same time, but writes get exclusive
334 rw=str Type of io pattern. Accepted values are:
336 read Sequential reads
337 write Sequential writes
338 randwrite Random writes
339 randread Random reads
340 rw,readwrite Sequential mixed reads and writes
341 randrw Random mixed reads and writes
343 For the mixed io types, the default is to split them 50/50.
344 For certain types of io the result may still be skewed a bit,
345 since the speed may be different. It is possible to specify
346 a number of IO's to do before getting a new offset, this is
347 one by appending a ':<nr>' to the end of the string given.
348 For a random read, it would look like 'rw=randread:8' for
349 passing in an offset modifier with a value of 8. If the
350 suffix is used with a sequential IO pattern, then the value
351 specified will be added to the generated offset for each IO.
352 For instance, using rw=write:4k will skip 4k for every
353 write. It turns sequential IO into sequential IO with holes.
354 See the 'rw_sequencer' option.
356 rw_sequencer=str If an offset modifier is given by appending a number to
357 the rw=<str> line, then this option controls how that
358 number modifies the IO offset being generated. Accepted
361 sequential Generate sequential offset
362 identical Generate the same offset
364 'sequential' is only useful for random IO, where fio would
365 normally generate a new random offset for every IO. If you
366 append eg 8 to randread, you would get a new random offset for
367 every 8 IO's. The result would be a seek for only every 8
368 IO's, instead of for every IO. Use rw=randread:8 to specify
369 that. As sequential IO is already sequential, setting
370 'sequential' for that would not result in any differences.
371 'identical' behaves in a similar fashion, except it sends
372 the same offset 8 number of times before generating a new
375 kb_base=int The base unit for a kilobyte. The defacto base is 2^10, 1024.
376 Storage manufacturers like to use 10^3 or 1000 as a base
377 ten unit instead, for obvious reasons. Allow values are
378 1024 or 1000, with 1024 being the default.
380 unified_rw_reporting=bool Fio normally reports statistics on a per
381 data direction basis, meaning that read, write, and trim are
382 accounted and reported separately. If this option is set,
383 the fio will sum the results and report them as "mixed"
386 randrepeat=bool For random IO workloads, seed the generator in a predictable
387 way so that results are repeatable across repetitions.
389 randseed=int Seed the random number generators based on this seed value, to
390 be able to control what sequence of output is being generated.
391 If not set, the random sequence depends on the randrepeat
394 use_os_rand=bool Fio can either use the random generator supplied by the OS
395 to generator random offsets, or it can use it's own internal
396 generator (based on Tausworthe). Default is to use the
397 internal generator, which is often of better quality and
400 fallocate=str Whether pre-allocation is performed when laying down files.
403 none Do not pre-allocate space
404 posix Pre-allocate via posix_fallocate()
405 keep Pre-allocate via fallocate() with
406 FALLOC_FL_KEEP_SIZE set
407 0 Backward-compatible alias for 'none'
408 1 Backward-compatible alias for 'posix'
410 May not be available on all supported platforms. 'keep' is only
411 available on Linux.If using ZFS on Solaris this must be set to
412 'none' because ZFS doesn't support it. Default: 'posix'.
414 fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
415 on what IO patterns it is likely to issue. Sometimes you
416 want to test specific IO patterns without telling the
417 kernel about it, in which case you can disable this option.
418 If set, fio will use POSIX_FADV_SEQUENTIAL for sequential
419 IO and POSIX_FADV_RANDOM for random IO.
421 size=int The total size of file io for this job. Fio will run until
422 this many bytes has been transferred, unless runtime is
423 limited by other options (such as 'runtime', for instance).
424 Unless specific nrfiles and filesize options are given,
425 fio will divide this size between the available files
426 specified by the job. If not set, fio will use the full
427 size of the given files or devices. If the files do not
428 exist, size must be given. It is also possible to give
429 size as a percentage between 1 and 100. If size=20% is
430 given, fio will use 20% of the full size of the given
433 io_limit=int Normally fio operates within the region set by 'size', which
434 means that the 'size' option sets both the region and size of
435 IO to be performed. Sometimes that is not what you want. With
436 this option, it is possible to define just the amount of IO
437 that fio should do. For instance, if 'size' is set to 20G and
438 'io_limit' is set to 5G, fio will perform IO within the first
439 20G but exit when 5G have been done.
441 filesize=int Individual file sizes. May be a range, in which case fio
442 will select sizes for files at random within the given range
443 and limited to 'size' in total (if that is given). If not
444 given, each created file is the same size.
446 file_append=bool Perform IO after the end of the file. Normally fio will
447 operate within the size of a file. If this option is set, then
448 fio will append to the file instead. This has identical
449 behavior to setting offset to the size of a file. This option
450 is ignored on non-regular files.
453 fill_fs=bool Sets size to something really large and waits for ENOSPC (no
454 space left on device) as the terminating condition. Only makes
455 sense with sequential write. For a read workload, the mount
456 point will be filled first then IO started on the result. This
457 option doesn't make sense if operating on a raw device node,
458 since the size of that is already known by the file system.
459 Additionally, writing beyond end-of-device will not return
463 bs=int The block size used for the io units. Defaults to 4k. Values
464 can be given for both read and writes. If a single int is
465 given, it will apply to both. If a second int is specified
466 after a comma, it will apply to writes only. In other words,
467 the format is either bs=read_and_write or bs=read,write,trim.
468 bs=4k,8k will thus use 4k blocks for reads, 8k blocks for
469 writes, and 8k for trims. You can terminate the list with
470 a trailing comma. bs=4k,8k, would use the default value for
471 trims.. If you only wish to set the write size, you
472 can do so by passing an empty read size - bs=,8k will set
473 8k for writes and leave the read default value.
476 ba=int At what boundary to align random IO offsets. Defaults to
477 the same as 'blocksize' the minimum blocksize given.
478 Minimum alignment is typically 512b for using direct IO,
479 though it usually depends on the hardware block size. This
480 option is mutually exclusive with using a random map for
481 files, so it will turn off that option.
483 blocksize_range=irange
484 bsrange=irange Instead of giving a single block size, specify a range
485 and fio will mix the issued io block sizes. The issued
486 io unit will always be a multiple of the minimum value
487 given (also see bs_unaligned). Applies to both reads and
488 writes, however a second range can be given after a comma.
491 bssplit=str Sometimes you want even finer grained control of the
492 block sizes issued, not just an even split between them.
493 This option allows you to weight various block sizes,
494 so that you are able to define a specific amount of
495 block sizes issued. The format for this option is:
497 bssplit=blocksize/percentage:blocksize/percentage
499 for as many block sizes as needed. So if you want to define
500 a workload that has 50% 64k blocks, 10% 4k blocks, and
501 40% 32k blocks, you would write:
503 bssplit=4k/10:64k/50:32k/40
505 Ordering does not matter. If the percentage is left blank,
506 fio will fill in the remaining values evenly. So a bssplit
507 option like this one:
509 bssplit=4k/50:1k/:32k/
511 would have 50% 4k ios, and 25% 1k and 32k ios. The percentages
512 always add up to 100, if bssplit is given a range that adds
513 up to more, it will error out.
515 bssplit also supports giving separate splits to reads and
516 writes. The format is identical to what bs= accepts. You
517 have to separate the read and write parts with a comma. So
518 if you want a workload that has 50% 2k reads and 50% 4k reads,
519 while having 90% 4k writes and 10% 8k writes, you would
522 bssplit=2k/50:4k/50,4k/90,8k/10
525 bs_unaligned If this option is given, any byte size value within bsrange
526 may be used as a block range. This typically wont work with
527 direct IO, as that normally requires sector alignment.
529 bs_is_seq_rand If this option is set, fio will use the normal read,write
530 blocksize settings as sequential,random instead. Any random
531 read or write will use the WRITE blocksize settings, and any
532 sequential read or write will use the READ blocksize setting.
534 zero_buffers If this option is given, fio will init the IO buffers to
535 all zeroes. The default is to fill them with random data.
536 The resulting IO buffers will not be completely zeroed,
537 unless scramble_buffers is also turned off.
539 refill_buffers If this option is given, fio will refill the IO buffers
540 on every submit. The default is to only fill it at init
541 time and reuse that data. Only makes sense if zero_buffers
542 isn't specified, naturally. If data verification is enabled,
543 refill_buffers is also automatically enabled.
545 scramble_buffers=bool If refill_buffers is too costly and the target is
546 using data deduplication, then setting this option will
547 slightly modify the IO buffer contents to defeat normal
548 de-dupe attempts. This is not enough to defeat more clever
549 block compression attempts, but it will stop naive dedupe of
550 blocks. Default: true.
552 buffer_compress_percentage=int If this is set, then fio will attempt to
553 provide IO buffer content (on WRITEs) that compress to
554 the specified level. Fio does this by providing a mix of
555 random data and zeroes. Note that this is per block size
556 unit, for file/disk wide compression level that matches
557 this setting, you'll also want to set refill_buffers.
559 buffer_compress_chunk=int See buffer_compress_percentage. This
560 setting allows fio to manage how big the ranges of random
561 data and zeroed data is. Without this set, fio will
562 provide buffer_compress_percentage of blocksize random
563 data, followed by the remaining zeroed. With this set
564 to some chunk size smaller than the block size, fio can
565 alternate random and zeroed data throughout the IO
568 buffer_pattern=str If set, fio will fill the io buffers with this pattern.
569 If not set, the contents of io buffers is defined by the other
570 options related to buffer contents. The setting can be any
571 pattern of bytes, and can be prefixed with 0x for hex values.
573 nrfiles=int Number of files to use for this job. Defaults to 1.
575 openfiles=int Number of files to keep open at the same time. Defaults to
576 the same as nrfiles, can be set smaller to limit the number
579 file_service_type=str Defines how fio decides which file from a job to
580 service next. The following types are defined:
582 random Just choose a file at random.
584 roundrobin Round robin over open files. This
587 sequential Finish one file before moving on to
588 the next. Multiple files can still be
589 open depending on 'openfiles'.
591 The string can have a number appended, indicating how
592 often to switch to a new file. So if option random:4 is
593 given, fio will switch to a new random file after 4 ios
596 ioengine=str Defines how the job issues io to the file. The following
599 sync Basic read(2) or write(2) io. lseek(2) is
600 used to position the io location.
602 psync Basic pread(2) or pwrite(2) io.
604 vsync Basic readv(2) or writev(2) IO.
606 psyncv Basic preadv(2) or pwritev(2) IO.
608 libaio Linux native asynchronous io. Note that Linux
609 may only support queued behaviour with
610 non-buffered IO (set direct=1 or buffered=0).
611 This engine defines engine specific options.
613 posixaio glibc posix asynchronous io.
615 solarisaio Solaris native asynchronous io.
617 windowsaio Windows native asynchronous io.
619 mmap File is memory mapped and data copied
620 to/from using memcpy(3).
622 splice splice(2) is used to transfer the data and
623 vmsplice(2) to transfer data from user
626 syslet-rw Use the syslet system calls to make
627 regular read/write async.
629 sg SCSI generic sg v3 io. May either be
630 synchronous using the SG_IO ioctl, or if
631 the target is an sg character device
632 we use read(2) and write(2) for asynchronous
635 null Doesn't transfer any data, just pretends
636 to. This is mainly used to exercise fio
637 itself and for debugging/testing purposes.
639 net Transfer over the network to given host:port.
640 Depending on the protocol used, the hostname,
641 port, listen and filename options are used to
642 specify what sort of connection to make, while
643 the protocol option determines which protocol
645 This engine defines engine specific options.
647 netsplice Like net, but uses splice/vmsplice to
648 map data and send/receive.
649 This engine defines engine specific options.
651 cpuio Doesn't transfer any data, but burns CPU
652 cycles according to the cpuload= and
653 cpucycle= options. Setting cpuload=85
654 will cause that job to do nothing but burn
655 85% of the CPU. In case of SMP machines,
656 use numjobs=<no_of_cpu> to get desired CPU
657 usage, as the cpuload only loads a single
658 CPU at the desired rate.
660 guasi The GUASI IO engine is the Generic Userspace
661 Asyncronous Syscall Interface approach
664 http://www.xmailserver.org/guasi-lib.html
666 for more info on GUASI.
668 rdma The RDMA I/O engine supports both RDMA
669 memory semantics (RDMA_WRITE/RDMA_READ) and
670 channel semantics (Send/Recv) for the
671 InfiniBand, RoCE and iWARP protocols.
673 falloc IO engine that does regular fallocate to
674 simulate data transfer as fio ioengine.
675 DDIR_READ does fallocate(,mode = keep_size,)
676 DDIR_WRITE does fallocate(,mode = 0)
677 DDIR_TRIM does fallocate(,mode = punch_hole)
679 e4defrag IO engine that does regular EXT4_IOC_MOVE_EXT
680 ioctls to simulate defragment activity in
681 request to DDIR_WRITE event
683 rbd IO engine supporting direct access to Ceph
684 Rados Block Devices (RBD) via librbd without
685 the need to use the kernel rbd driver. This
686 ioengine defines engine specific options.
688 gfapi Using Glusterfs libgfapi sync interface to
689 direct access to Glusterfs volumes without
692 gfapi_async Using Glusterfs libgfapi async interface
693 to direct access to Glusterfs volumes without
694 having to go through FUSE. This ioengine
695 defines engine specific options.
697 libhdfs Read and write through Hadoop (HDFS).
698 The 'filename' option is used to specify host,
699 port of the hdfs name-node to connect. This
700 engine interprets offsets a little
701 differently. In HDFS, files once created
702 cannot be modified. So random writes are not
703 possible. To imitate this, libhdfs engine
704 expects bunch of small files to be created
705 over HDFS, and engine will randomly pick a
706 file out of those files based on the offset
707 generated by fio backend. (see the example
708 job file to create such files, use rw=write
709 option). Please note, you might want to set
710 necessary environment variables to work with
711 hdfs/libhdfs properly.
713 external Prefix to specify loading an external
714 IO engine object file. Append the engine
715 filename, eg ioengine=external:/tmp/foo.o
716 to load ioengine foo.o in /tmp.
718 iodepth=int This defines how many io units to keep in flight against
719 the file. The default is 1 for each file defined in this
720 job, can be overridden with a larger value for higher
721 concurrency. Note that increasing iodepth beyond 1 will not
722 affect synchronous ioengines (except for small degress when
723 verify_async is in use). Even async engines may impose OS
724 restrictions causing the desired depth not to be achieved.
725 This may happen on Linux when using libaio and not setting
726 direct=1, since buffered IO is not async on that OS. Keep an
727 eye on the IO depth distribution in the fio output to verify
728 that the achieved depth is as expected. Default: 1.
730 iodepth_batch_submit=int
731 iodepth_batch=int This defines how many pieces of IO to submit at once.
732 It defaults to 1 which means that we submit each IO
733 as soon as it is available, but can be raised to submit
734 bigger batches of IO at the time.
736 iodepth_batch_complete=int This defines how many pieces of IO to retrieve
737 at once. It defaults to 1 which means that we'll ask
738 for a minimum of 1 IO in the retrieval process from
739 the kernel. The IO retrieval will go on until we
740 hit the limit set by iodepth_low. If this variable is
741 set to 0, then fio will always check for completed
742 events before queuing more IO. This helps reduce
743 IO latency, at the cost of more retrieval system calls.
745 iodepth_low=int The low water mark indicating when to start filling
746 the queue again. Defaults to the same as iodepth, meaning
747 that fio will attempt to keep the queue full at all times.
748 If iodepth is set to eg 16 and iodepth_low is set to 4, then
749 after fio has filled the queue of 16 requests, it will let
750 the depth drain down to 4 before starting to fill it again.
752 direct=bool If value is true, use non-buffered io. This is usually
753 O_DIRECT. Note that ZFS on Solaris doesn't support direct io.
754 On Windows the synchronous ioengines don't support direct io.
756 atomic=bool If value is true, attempt to use atomic direct IO. Atomic
757 writes are guaranteed to be stable once acknowledged by
758 the operating system. Only Linux supports O_ATOMIC right
761 buffered=bool If value is true, use buffered io. This is the opposite
762 of the 'direct' option. Defaults to true.
764 offset=int Start io at the given offset in the file. The data before
765 the given offset will not be touched. This effectively
766 caps the file size at real_size - offset.
768 offset_increment=int If this is provided, then the real offset becomes
769 offset + offset_increment * thread_number, where the thread
770 number is a counter that starts at 0 and is incremented for
771 each sub-job (i.e. when numjobs option is specified). This
772 option is useful if there are several jobs which are intended
773 to operate on a file in parallel disjoint segments, with
774 even spacing between the starting points.
776 number_ios=int Fio will normally perform IOs until it has exhausted the size
777 of the region set by size=, or if it exhaust the allocated
778 time (or hits an error condition). With this setting, the
779 range/size can be set independently of the number of IOs to
780 perform. When fio reaches this number, it will exit normally
783 fsync=int If writing to a file, issue a sync of the dirty data
784 for every number of blocks given. For example, if you give
785 32 as a parameter, fio will sync the file for every 32
786 writes issued. If fio is using non-buffered io, we may
787 not sync the file. The exception is the sg io engine, which
788 synchronizes the disk cache anyway.
790 fdatasync=int Like fsync= but uses fdatasync() to only sync data and not
792 In FreeBSD and Windows there is no fdatasync(), this falls back to
795 sync_file_range=str:val Use sync_file_range() for every 'val' number of
796 write operations. Fio will track range of writes that
797 have happened since the last sync_file_range() call. 'str'
798 can currently be one or more of:
800 wait_before SYNC_FILE_RANGE_WAIT_BEFORE
801 write SYNC_FILE_RANGE_WRITE
802 wait_after SYNC_FILE_RANGE_WAIT_AFTER
804 So if you do sync_file_range=wait_before,write:8, fio would
805 use SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE for
806 every 8 writes. Also see the sync_file_range(2) man page.
807 This option is Linux specific.
809 overwrite=bool If true, writes to a file will always overwrite existing
810 data. If the file doesn't already exist, it will be
811 created before the write phase begins. If the file exists
812 and is large enough for the specified write phase, nothing
815 end_fsync=bool If true, fsync file contents when a write stage has completed.
817 fsync_on_close=bool If true, fio will fsync() a dirty file on close.
818 This differs from end_fsync in that it will happen on every
819 file close, not just at the end of the job.
821 rwmixread=int How large a percentage of the mix should be reads.
823 rwmixwrite=int How large a percentage of the mix should be writes. If both
824 rwmixread and rwmixwrite is given and the values do not add
825 up to 100%, the latter of the two will be used to override
826 the first. This may interfere with a given rate setting,
827 if fio is asked to limit reads or writes to a certain rate.
828 If that is the case, then the distribution may be skewed.
830 random_distribution=str:float By default, fio will use a completely uniform
831 random distribution when asked to perform random IO. Sometimes
832 it is useful to skew the distribution in specific ways,
833 ensuring that some parts of the data is more hot than others.
834 fio includes the following distribution models:
836 random Uniform random distribution
837 zipf Zipf distribution
838 pareto Pareto distribution
840 When using a zipf or pareto distribution, an input value
841 is also needed to define the access pattern. For zipf, this
842 is the zipf theta. For pareto, it's the pareto power. Fio
843 includes a test program, genzipf, that can be used visualize
844 what the given input values will yield in terms of hit rates.
845 If you wanted to use zipf with a theta of 1.2, you would use
846 random_distribution=zipf:1.2 as the option. If a non-uniform
847 model is used, fio will disable use of the random map.
849 percentage_random=int For a random workload, set how big a percentage should
850 be random. This defaults to 100%, in which case the workload
851 is fully random. It can be set from anywhere from 0 to 100.
852 Setting it to 0 would make the workload fully sequential. Any
853 setting in between will result in a random mix of sequential
854 and random IO, at the given percentages. It is possible to
855 set different values for reads, writes, and trim. To do so,
856 simply use a comma separated list. See blocksize.
858 norandommap Normally fio will cover every block of the file when doing
859 random IO. If this option is given, fio will just get a
860 new random offset without looking at past io history. This
861 means that some blocks may not be read or written, and that
862 some blocks may be read/written more than once. This option
863 is mutually exclusive with verify= if and only if multiple
864 blocksizes (via bsrange=) are used, since fio only tracks
865 complete rewrites of blocks.
867 softrandommap=bool See norandommap. If fio runs with the random block map
868 enabled and it fails to allocate the map, if this option is
869 set it will continue without a random block map. As coverage
870 will not be as complete as with random maps, this option is
873 random_generator=str Fio supports the following engines for generating
874 IO offsets for random IO:
876 tausworthe Strong 2^88 cycle random number generator
877 lfsr Linear feedback shift register generator
879 Tausworthe is a strong random number generator, but it
880 requires tracking on the side if we want to ensure that
881 blocks are only read or written once. LFSR guarantees
882 that we never generate the same offset twice, and it's
883 also less computationally expensive. It's not a true
884 random generator, however, though for IO purposes it's
885 typically good enough. LFSR only works with single
886 block sizes, not with workloads that use multiple block
887 sizes. If used with such a workload, fio may read or write
888 some blocks multiple times.
890 nice=int Run the job with the given nice value. See man nice(2).
892 prio=int Set the io priority value of this job. Linux limits us to
893 a positive value between 0 and 7, with 0 being the highest.
896 prioclass=int Set the io priority class. See man ionice(1).
898 thinktime=int Stall the job x microseconds after an io has completed before
899 issuing the next. May be used to simulate processing being
900 done by an application. See thinktime_blocks and
904 Only valid if thinktime is set - pretend to spend CPU time
905 doing something with the data received, before falling back
906 to sleeping for the rest of the period specified by
910 Only valid if thinktime is set - control how many blocks
911 to issue, before waiting 'thinktime' usecs. If not set,
912 defaults to 1 which will make fio wait 'thinktime' usecs
913 after every block. This effectively makes any queue depth
914 setting redundant, since no more than 1 IO will be queued
915 before we have to complete it and do our thinktime. In
916 other words, this setting effectively caps the queue depth
917 if the latter is larger.
919 rate=int Cap the bandwidth used by this job. The number is in bytes/sec,
920 the normal suffix rules apply. You can use rate=500k to limit
921 reads and writes to 500k each, or you can specify read and
922 writes separately. Using rate=1m,500k would limit reads to
923 1MB/sec and writes to 500KB/sec. Capping only reads or
924 writes can be done with rate=,500k or rate=500k,. The former
925 will only limit writes (to 500KB/sec), the latter will only
928 ratemin=int Tell fio to do whatever it can to maintain at least this
929 bandwidth. Failing to meet this requirement, will cause
930 the job to exit. The same format as rate is used for
931 read vs write separation.
933 rate_iops=int Cap the bandwidth to this number of IOPS. Basically the same
934 as rate, just specified independently of bandwidth. If the
935 job is given a block size range instead of a fixed value,
936 the smallest block size is used as the metric. The same format
937 as rate is used for read vs write separation.
939 rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
940 the job to exit. The same format as rate is used for read vs
943 latency_target=int If set, fio will attempt to find the max performance
944 point that the given workload will run at while maintaining a
945 latency below this target. The values is given in microseconds.
946 See latency_window and latency_percentile
948 latency_window=int Used with latency_target to specify the sample window
949 that the job is run at varying queue depths to test the
950 performance. The value is given in microseconds.
952 latency_percentile=float The percentage of IOs that must fall within the
953 criteria specified by latency_target and latency_window. If not
954 set, this defaults to 100.0, meaning that all IOs must be equal
955 or below to the value set by latency_target.
957 max_latency=int If set, fio will exit the job if it exceeds this maximum
958 latency. It will exit with an ETIME error.
960 ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
963 cpumask=int Set the CPU affinity of this job. The parameter given is a
964 bitmask of allowed CPU's the job may run on. So if you want
965 the allowed CPUs to be 1 and 5, you would pass the decimal
966 value of (1 << 1 | 1 << 5), or 34. See man
967 sched_setaffinity(2). This may not work on all supported
968 operating systems or kernel versions. This option doesn't
969 work well for a higher CPU count than what you can store in
970 an integer mask, so it can only control cpus 1-32. For
971 boxes with larger CPU counts, use cpus_allowed.
973 cpus_allowed=str Controls the same options as cpumask, but it allows a text
974 setting of the permitted CPUs instead. So to use CPUs 1 and
975 5, you would specify cpus_allowed=1,5. This options also
976 allows a range of CPUs. Say you wanted a binding to CPUs
977 1, 5, and 8-15, you would set cpus_allowed=1,5,8-15.
979 cpus_allowed_policy=str Set the policy of how fio distributes the CPUs
980 specified by cpus_allowed or cpumask. Two policies are
983 shared All jobs will share the CPU set specified.
984 split Each job will get a unique CPU from the CPU set.
986 'shared' is the default behaviour, if the option isn't
987 specified. If split is specified, then fio will will assign
988 one cpu per job. If not enough CPUs are given for the jobs
989 listed, then fio will roundrobin the CPUs in the set.
991 numa_cpu_nodes=str Set this job running on spcified NUMA nodes' CPUs. The
992 arguments allow comma delimited list of cpu numbers,
993 A-B ranges, or 'all'. Note, to enable numa options support,
994 fio must be built on a system with libnuma-dev(el) installed.
996 numa_mem_policy=str Set this job's memory policy and corresponding NUMA
997 nodes. Format of the argements:
999 `mode' is one of the following memory policy:
1000 default, prefer, bind, interleave, local
1001 For `default' and `local' memory policy, no node is
1002 needed to be specified.
1003 For `prefer', only one node is allowed.
1004 For `bind' and `interleave', it allow comma delimited
1005 list of numbers, A-B ranges, or 'all'.
1007 startdelay=time Start this job the specified number of seconds after fio
1008 has started. Only useful if the job file contains several
1009 jobs, and you want to delay starting some jobs to a certain
1012 runtime=time Tell fio to terminate processing after the specified number
1013 of seconds. It can be quite hard to determine for how long
1014 a specified job will run, so this parameter is handy to
1015 cap the total runtime to a given time.
1017 time_based If set, fio will run for the duration of the runtime
1018 specified even if the file(s) are completely read or
1019 written. It will simply loop over the same workload
1020 as many times as the runtime allows.
1022 ramp_time=time If set, fio will run the specified workload for this amount
1023 of time before logging any performance numbers. Useful for
1024 letting performance settle before logging results, thus
1025 minimizing the runtime required for stable results. Note
1026 that the ramp_time is considered lead in time for a job,
1027 thus it will increase the total runtime if a special timeout
1028 or runtime is specified.
1030 invalidate=bool Invalidate the buffer/page cache parts for this file prior
1031 to starting io. Defaults to true.
1033 sync=bool Use sync io for buffered writes. For the majority of the
1034 io engines, this means using O_SYNC.
1037 mem=str Fio can use various types of memory as the io unit buffer.
1038 The allowed values are:
1040 malloc Use memory from malloc(3) as the buffers.
1042 shm Use shared memory as the buffers. Allocated
1045 shmhuge Same as shm, but use huge pages as backing.
1047 mmap Use mmap to allocate buffers. May either be
1048 anonymous memory, or can be file backed if
1049 a filename is given after the option. The
1050 format is mem=mmap:/path/to/file.
1052 mmaphuge Use a memory mapped huge file as the buffer
1053 backing. Append filename after mmaphuge, ala
1054 mem=mmaphuge:/hugetlbfs/file
1056 The area allocated is a function of the maximum allowed
1057 bs size for the job, multiplied by the io depth given. Note
1058 that for shmhuge and mmaphuge to work, the system must have
1059 free huge pages allocated. This can normally be checked
1060 and set by reading/writing /proc/sys/vm/nr_hugepages on a
1061 Linux system. Fio assumes a huge page is 4MB in size. So
1062 to calculate the number of huge pages you need for a given
1063 job file, add up the io depth of all jobs (normally one unless
1064 iodepth= is used) and multiply by the maximum bs set. Then
1065 divide that number by the huge page size. You can see the
1066 size of the huge pages in /proc/meminfo. If no huge pages
1067 are allocated by having a non-zero number in nr_hugepages,
1068 using mmaphuge or shmhuge will fail. Also see hugepage-size.
1070 mmaphuge also needs to have hugetlbfs mounted and the file
1071 location should point there. So if it's mounted in /huge,
1072 you would use mem=mmaphuge:/huge/somefile.
1074 iomem_align=int This indiciates the memory alignment of the IO memory buffers.
1075 Note that the given alignment is applied to the first IO unit
1076 buffer, if using iodepth the alignment of the following buffers
1077 are given by the bs used. In other words, if using a bs that is
1078 a multiple of the page sized in the system, all buffers will
1079 be aligned to this value. If using a bs that is not page
1080 aligned, the alignment of subsequent IO memory buffers is the
1081 sum of the iomem_align and bs used.
1084 Defines the size of a huge page. Must at least be equal
1085 to the system setting, see /proc/meminfo. Defaults to 4MB.
1086 Should probably always be a multiple of megabytes, so using
1087 hugepage-size=Xm is the preferred way to set this to avoid
1088 setting a non-pow-2 bad value.
1090 exitall When one job finishes, terminate the rest. The default is
1091 to wait for each job to finish, sometimes that is not the
1094 bwavgtime=int Average the calculated bandwidth over the given time. Value
1095 is specified in milliseconds.
1097 iopsavgtime=int Average the calculated IOPS over the given time. Value
1098 is specified in milliseconds.
1100 create_serialize=bool If true, serialize the file creating for the jobs.
1101 This may be handy to avoid interleaving of data
1102 files, which may greatly depend on the filesystem
1103 used and even the number of processors in the system.
1105 create_fsync=bool fsync the data file after creation. This is the
1108 create_on_open=bool Don't pre-setup the files for IO, just create open()
1109 when it's time to do IO to that file.
1111 create_only=bool If true, fio will only run the setup phase of the job.
1112 If files need to be laid out or updated on disk, only
1113 that will be done. The actual job contents are not
1116 pre_read=bool If this is given, files will be pre-read into memory before
1117 starting the given IO operation. This will also clear
1118 the 'invalidate' flag, since it is pointless to pre-read
1119 and then drop the cache. This will only work for IO engines
1120 that are seekable, since they allow you to read the same data
1121 multiple times. Thus it will not work on eg network or splice
1124 unlink=bool Unlink the job files when done. Not the default, as repeated
1125 runs of that job would then waste time recreating the file
1126 set again and again.
1128 loops=int Run the specified number of iterations of this job. Used
1129 to repeat the same workload a given number of times. Defaults
1132 verify_only Do not perform specified workload---only verify data still
1133 matches previous invocation of this workload. This option
1134 allows one to check data multiple times at a later date
1135 without overwriting it. This option makes sense only for
1136 workloads that write data, and does not support workloads
1137 with the time_based option set.
1139 do_verify=bool Run the verify phase after a write phase. Only makes sense if
1140 verify is set. Defaults to 1.
1142 verify=str If writing to a file, fio can verify the file contents
1143 after each iteration of the job. The allowed values are:
1145 md5 Use an md5 sum of the data area and store
1146 it in the header of each block.
1148 crc64 Use an experimental crc64 sum of the data
1149 area and store it in the header of each
1152 crc32c Use a crc32c sum of the data area and store
1153 it in the header of each block.
1155 crc32c-intel Use hardware assisted crc32c calcuation
1156 provided on SSE4.2 enabled processors. Falls
1157 back to regular software crc32c, if not
1158 supported by the system.
1160 crc32 Use a crc32 sum of the data area and store
1161 it in the header of each block.
1163 crc16 Use a crc16 sum of the data area and store
1164 it in the header of each block.
1166 crc7 Use a crc7 sum of the data area and store
1167 it in the header of each block.
1169 xxhash Use xxhash as the checksum function. Generally
1170 the fastest software checksum that fio
1173 sha512 Use sha512 as the checksum function.
1175 sha256 Use sha256 as the checksum function.
1177 sha1 Use optimized sha1 as the checksum function.
1179 meta Write extra information about each io
1180 (timestamp, block number etc.). The block
1181 number is verified. The io sequence number is
1182 verified for workloads that write data.
1183 See also verify_pattern.
1185 null Only pretend to verify. Useful for testing
1186 internals with ioengine=null, not for much
1189 This option can be used for repeated burn-in tests of a
1190 system to make sure that the written data is also
1191 correctly read back. If the data direction given is
1192 a read or random read, fio will assume that it should
1193 verify a previously written file. If the data direction
1194 includes any form of write, the verify will be of the
1197 verifysort=bool If set, fio will sort written verify blocks when it deems
1198 it faster to read them back in a sorted manner. This is
1199 often the case when overwriting an existing file, since
1200 the blocks are already laid out in the file system. You
1201 can ignore this option unless doing huge amounts of really
1202 fast IO where the red-black tree sorting CPU time becomes
1205 verify_offset=int Swap the verification header with data somewhere else
1206 in the block before writing. Its swapped back before
1209 verify_interval=int Write the verification header at a finer granularity
1210 than the blocksize. It will be written for chunks the
1211 size of header_interval. blocksize should divide this
1214 verify_pattern=str If set, fio will fill the io buffers with this
1215 pattern. Fio defaults to filling with totally random
1216 bytes, but sometimes it's interesting to fill with a known
1217 pattern for io verification purposes. Depending on the
1218 width of the pattern, fio will fill 1/2/3/4 bytes of the
1219 buffer at the time(it can be either a decimal or a hex number).
1220 The verify_pattern if larger than a 32-bit quantity has to
1221 be a hex number that starts with either "0x" or "0X". Use
1224 verify_fatal=bool Normally fio will keep checking the entire contents
1225 before quitting on a block verification failure. If this
1226 option is set, fio will exit the job on the first observed
1229 verify_dump=bool If set, dump the contents of both the original data
1230 block and the data block we read off disk to files. This
1231 allows later analysis to inspect just what kind of data
1232 corruption occurred. Off by default.
1234 verify_async=int Fio will normally verify IO inline from the submitting
1235 thread. This option takes an integer describing how many
1236 async offload threads to create for IO verification instead,
1237 causing fio to offload the duty of verifying IO contents
1238 to one or more separate threads. If using this offload
1239 option, even sync IO engines can benefit from using an
1240 iodepth setting higher than 1, as it allows them to have
1241 IO in flight while verifies are running.
1243 verify_async_cpus=str Tell fio to set the given CPU affinity on the
1244 async IO verification threads. See cpus_allowed for the
1247 verify_backlog=int Fio will normally verify the written contents of a
1248 job that utilizes verify once that job has completed. In
1249 other words, everything is written then everything is read
1250 back and verified. You may want to verify continually
1251 instead for a variety of reasons. Fio stores the meta data
1252 associated with an IO block in memory, so for large
1253 verify workloads, quite a bit of memory would be used up
1254 holding this meta data. If this option is enabled, fio
1255 will write only N blocks before verifying these blocks.
1257 verify_backlog_batch=int Control how many blocks fio will verify
1258 if verify_backlog is set. If not set, will default to
1259 the value of verify_backlog (meaning the entire queue
1260 is read back and verified). If verify_backlog_batch is
1261 less than verify_backlog then not all blocks will be verified,
1262 if verify_backlog_batch is larger than verify_backlog, some
1263 blocks will be verified more than once.
1266 wait_for_previous Wait for preceding jobs in the job file to exit, before
1267 starting this one. Can be used to insert serialization
1268 points in the job file. A stone wall also implies starting
1269 a new reporting group.
1271 new_group Start a new reporting group. See: group_reporting.
1273 numjobs=int Create the specified number of clones of this job. May be
1274 used to setup a larger number of threads/processes doing
1275 the same thing. Each thread is reported separately; to see
1276 statistics for all clones as a whole, use group_reporting in
1277 conjunction with new_group.
1279 group_reporting It may sometimes be interesting to display statistics for
1280 groups of jobs as a whole instead of for each individual job.
1281 This is especially true if 'numjobs' is used; looking at
1282 individual thread/process output quickly becomes unwieldy.
1283 To see the final report per-group instead of per-job, use
1284 'group_reporting'. Jobs in a file will be part of the same
1285 reporting group, unless if separated by a stonewall, or by
1288 thread fio defaults to forking jobs, however if this option is
1289 given, fio will use pthread_create(3) to create threads
1292 zonesize=int Divide a file into zones of the specified size. See zoneskip.
1294 zoneskip=int Skip the specified number of bytes when zonesize data has
1295 been read. The two zone options can be used to only do
1296 io on zones of a file.
1298 write_iolog=str Write the issued io patterns to the specified file. See
1299 read_iolog. Specify a separate file for each job, otherwise
1300 the iologs will be interspersed and the file may be corrupt.
1302 read_iolog=str Open an iolog with the specified file name and replay the
1303 io patterns it contains. This can be used to store a
1304 workload and replay it sometime later. The iolog given
1305 may also be a blktrace binary file, which allows fio
1306 to replay a workload captured by blktrace. See blktrace
1307 for how to capture such logging data. For blktrace replay,
1308 the file needs to be turned into a blkparse binary data
1309 file first (blkparse <device> -o /dev/null -d file_for_fio.bin).
1311 replay_no_stall=int When replaying I/O with read_iolog the default behavior
1312 is to attempt to respect the time stamps within the log and
1313 replay them with the appropriate delay between IOPS. By
1314 setting this variable fio will not respect the timestamps and
1315 attempt to replay them as fast as possible while still
1316 respecting ordering. The result is the same I/O pattern to a
1317 given device, but different timings.
1319 replay_redirect=str While replaying I/O patterns using read_iolog the
1320 default behavior is to replay the IOPS onto the major/minor
1321 device that each IOP was recorded from. This is sometimes
1322 undesirable because on a different machine those major/minor
1323 numbers can map to a different device. Changing hardware on
1324 the same system can also result in a different major/minor
1325 mapping. Replay_redirect causes all IOPS to be replayed onto
1326 the single specified device regardless of the device it was
1327 recorded from. i.e. replay_redirect=/dev/sdc would cause all
1328 IO in the blktrace to be replayed onto /dev/sdc. This means
1329 multiple devices will be replayed onto a single, if the trace
1330 contains multiple devices. If you want multiple devices to be
1331 replayed concurrently to multiple redirected devices you must
1332 blkparse your trace into separate traces and replay them with
1333 independent fio invocations. Unfortuantely this also breaks
1334 the strict time ordering between multiple device accesses.
1336 write_bw_log=str If given, write a bandwidth log of the jobs in this job
1337 file. Can be used to store data of the bandwidth of the
1338 jobs in their lifetime. The included fio_generate_plots
1339 script uses gnuplot to turn these text files into nice
1340 graphs. See write_lat_log for behaviour of given
1341 filename. For this option, the suffix is _bw.x.log, where
1342 x is the index of the job (1..N, where N is the number of
1345 write_lat_log=str Same as write_bw_log, except that this option stores io
1346 submission, completion, and total latencies instead. If no
1347 filename is given with this option, the default filename of
1348 "jobname_type.log" is used. Even if the filename is given,
1349 fio will still append the type of log. So if one specifies
1353 The actual log names will be foo_slat.x.log, foo_clat.x.log,
1354 and foo_lat.x.log, where x is the index of the job (1..N,
1355 where N is the number of jobs). This helps fio_generate_plot
1356 fine the logs automatically.
1358 write_iops_log=str Same as write_bw_log, but writes IOPS. If no filename is
1359 given with this option, the default filename of
1360 "jobname_type.x.log" is used,where x is the index of the job
1361 (1..N, where N is the number of jobs). Even if the filename
1362 is given, fio will still append the type of log.
1364 log_avg_msec=int By default, fio will log an entry in the iops, latency,
1365 or bw log for every IO that completes. When writing to the
1366 disk log, that can quickly grow to a very large size. Setting
1367 this option makes fio average the each log entry over the
1368 specified period of time, reducing the resolution of the log.
1371 log_offset=int If this is set, the iolog options will include the byte
1372 offset for the IO entry as well as the other data values.
1374 log_compression=int If this is set, fio will compress the IO logs as
1375 it goes, to keep the memory footprint lower. When a log
1376 reaches the specified size, that chunk is removed and
1377 compressed in the background. Given that IO logs are
1378 fairly highly compressible, this yields a nice memory
1379 savings for longer runs. The downside is that the
1380 compression will consume some background CPU cycles, so
1381 it may impact the run. This, however, is also true if
1382 the logging ends up consuming most of the system memory.
1383 So pick your poison. The IO logs are saved normally at the
1384 end of a run, by decompressing the chunks and storing them
1385 in the specified log file. This feature depends on the
1386 availability of zlib.
1388 log_store_compressed=bool If set, and log_compression is also set,
1389 fio will store the log files in a compressed format. They
1390 can be decompressed with fio, using the --inflate-log
1391 command line parameter. The files will be stored with a
1394 lockmem=int Pin down the specified amount of memory with mlock(2). Can
1395 potentially be used instead of removing memory or booting
1396 with less memory to simulate a smaller amount of memory.
1397 The amount specified is per worker.
1399 exec_prerun=str Before running this job, issue the command specified
1400 through system(3). Output is redirected in a file called
1403 exec_postrun=str After the job completes, issue the command specified
1404 though system(3). Output is redirected in a file called
1405 jobname.postrun.txt.
1407 ioscheduler=str Attempt to switch the device hosting the file to the specified
1408 io scheduler before running.
1410 disk_util=bool Generate disk utilization statistics, if the platform
1411 supports it. Defaults to on.
1413 disable_lat=bool Disable measurements of total latency numbers. Useful
1414 only for cutting back the number of calls to gettimeofday,
1415 as that does impact performance at really high IOPS rates.
1416 Note that to really get rid of a large amount of these
1417 calls, this option must be used with disable_slat and
1420 disable_clat=bool Disable measurements of completion latency numbers. See
1423 disable_slat=bool Disable measurements of submission latency numbers. See
1426 disable_bw=bool Disable measurements of throughput/bandwidth numbers. See
1429 clat_percentiles=bool Enable the reporting of percentiles of
1430 completion latencies.
1432 percentile_list=float_list Overwrite the default list of percentiles
1433 for completion latencies. Each number is a floating
1434 number in the range (0,100], and the maximum length of
1435 the list is 20. Use ':' to separate the numbers, and
1436 list the numbers in ascending order. For example,
1437 --percentile_list=99.5:99.9 will cause fio to report
1438 the values of completion latency below which 99.5% and
1439 99.9% of the observed latencies fell, respectively.
1441 clocksource=str Use the given clocksource as the base of timing. The
1442 supported options are:
1444 gettimeofday gettimeofday(2)
1446 clock_gettime clock_gettime(2)
1448 cpu Internal CPU clock source
1450 cpu is the preferred clocksource if it is reliable, as it
1451 is very fast (and fio is heavy on time calls). Fio will
1452 automatically use this clocksource if it's supported and
1453 considered reliable on the system it is running on, unless
1454 another clocksource is specifically set. For x86/x86-64 CPUs,
1455 this means supporting TSC Invariant.
1457 gtod_reduce=bool Enable all of the gettimeofday() reducing options
1458 (disable_clat, disable_slat, disable_bw) plus reduce
1459 precision of the timeout somewhat to really shrink
1460 the gettimeofday() call count. With this option enabled,
1461 we only do about 0.4% of the gtod() calls we would have
1462 done if all time keeping was enabled.
1464 gtod_cpu=int Sometimes it's cheaper to dedicate a single thread of
1465 execution to just getting the current time. Fio (and
1466 databases, for instance) are very intensive on gettimeofday()
1467 calls. With this option, you can set one CPU aside for
1468 doing nothing but logging current time to a shared memory
1469 location. Then the other threads/processes that run IO
1470 workloads need only copy that segment, instead of entering
1471 the kernel with a gettimeofday() call. The CPU set aside
1472 for doing these time calls will be excluded from other
1473 uses. Fio will manually clear it from the CPU mask of other
1476 continue_on_error=str Normally fio will exit the job on the first observed
1477 failure. If this option is set, fio will continue the job when
1478 there is a 'non-fatal error' (EIO or EILSEQ) until the runtime
1479 is exceeded or the I/O size specified is completed. If this
1480 option is used, there are two more stats that are appended,
1481 the total error count and the first error. The error field
1482 given in the stats is the first error that was hit during the
1485 The allowed values are:
1487 none Exit on any IO or verify errors.
1489 read Continue on read errors, exit on all others.
1491 write Continue on write errors, exit on all others.
1493 io Continue on any IO error, exit on all others.
1495 verify Continue on verify errors, exit on all others.
1497 all Continue on all errors.
1499 0 Backward-compatible alias for 'none'.
1501 1 Backward-compatible alias for 'all'.
1503 ignore_error=str Sometimes you want to ignore some errors during test
1504 in that case you can specify error list for each error type.
1505 ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST
1506 errors for given error type is separated with ':'. Error
1507 may be symbol ('ENOSPC', 'ENOMEM') or integer.
1509 ignore_error=EAGAIN,ENOSPC:122
1510 This option will ignore EAGAIN from READ, and ENOSPC and
1511 122(EDQUOT) from WRITE.
1513 error_dump=bool If set dump every error even if it is non fatal, true
1514 by default. If disabled only fatal error will be dumped
1516 cgroup=str Add job to this control group. If it doesn't exist, it will
1517 be created. The system must have a mounted cgroup blkio
1518 mount point for this to work. If your system doesn't have it
1519 mounted, you can do so with:
1521 # mount -t cgroup -o blkio none /cgroup
1523 cgroup_weight=int Set the weight of the cgroup to this value. See
1524 the documentation that comes with the kernel, allowed values
1525 are in the range of 100..1000.
1527 cgroup_nodelete=bool Normally fio will delete the cgroups it has created after
1528 the job completion. To override this behavior and to leave
1529 cgroups around after the job completion, set cgroup_nodelete=1.
1530 This can be useful if one wants to inspect various cgroup
1531 files after job completion. Default: false
1533 uid=int Instead of running as the invoking user, set the user ID to
1534 this value before the thread/process does any work.
1536 gid=int Set group ID, see uid.
1538 flow_id=int The ID of the flow. If not specified, it defaults to being a
1539 global flow. See flow.
1541 flow=int Weight in token-based flow control. If this value is used, then
1542 there is a 'flow counter' which is used to regulate the
1543 proportion of activity between two or more jobs. fio attempts
1544 to keep this flow counter near zero. The 'flow' parameter
1545 stands for how much should be added or subtracted to the flow
1546 counter on each iteration of the main I/O loop. That is, if
1547 one job has flow=8 and another job has flow=-1, then there
1548 will be a roughly 1:8 ratio in how much one runs vs the other.
1550 flow_watermark=int The maximum value that the absolute value of the flow
1551 counter is allowed to reach before the job must wait for a
1552 lower value of the counter.
1554 flow_sleep=int The period of time, in microseconds, to wait after the flow
1555 watermark has been exceeded before retrying operations
1557 In addition, there are some parameters which are only valid when a specific
1558 ioengine is in use. These are used identically to normal parameters, with the
1559 caveat that when used on the command line, they must come after the ioengine
1560 that defines them is selected.
1562 [libaio] userspace_reap Normally, with the libaio engine in use, fio will use
1563 the io_getevents system call to reap newly returned events.
1564 With this flag turned on, the AIO ring will be read directly
1565 from user-space to reap events. The reaping mode is only
1566 enabled when polling for a minimum of 0 events (eg when
1567 iodepth_batch_complete=0).
1569 [cpu] cpuload=int Attempt to use the specified percentage of CPU cycles.
1571 [cpu] cpuchunks=int Split the load into cycles of the given time. In
1574 [cpu] exit_on_io_done=bool Detect when IO threads are done, then exit.
1576 [netsplice] hostname=str
1577 [net] hostname=str The host name or IP address to use for TCP or UDP based IO.
1578 If the job is a TCP listener or UDP reader, the hostname is not
1579 used and must be omitted unless it is a valid UDP multicast
1582 [netsplice] port=int
1583 [net] port=int The TCP or UDP port to bind to or connect to.
1585 [netsplice] interface=str
1586 [net] interface=str The IP address of the network interface used to send or
1587 receive UDP multicast
1590 [net] ttl=int Time-to-live value for outgoing UDP multicast packets.
1593 [netsplice] nodelay=bool
1594 [net] nodelay=bool Set TCP_NODELAY on TCP connections.
1596 [netsplice] protocol=str
1597 [netsplice] proto=str
1599 [net] proto=str The network protocol to use. Accepted values are:
1601 tcp Transmission control protocol
1602 tcpv6 Transmission control protocol V6
1603 udp User datagram protocol
1604 udpv6 User datagram protocol V6
1605 unix UNIX domain socket
1607 When the protocol is TCP or UDP, the port must also be given,
1608 as well as the hostname if the job is a TCP listener or UDP
1609 reader. For unix sockets, the normal filename option should be
1610 used and the port is invalid.
1612 [net] listen For TCP network connections, tell fio to listen for incoming
1613 connections rather than initiating an outgoing connection. The
1614 hostname must be omitted if this option is used.
1615 [net] pingpong Normaly a network writer will just continue writing data, and
1616 a network reader will just consume packages. If pingpong=1
1617 is set, a writer will send its normal payload to the reader,
1618 then wait for the reader to send the same payload back. This
1619 allows fio to measure network latencies. The submission
1620 and completion latencies then measure local time spent
1621 sending or receiving, and the completion latency measures
1622 how long it took for the other end to receive and send back.
1623 For UDP multicast traffic pingpong=1 should only be set for a
1624 single reader when multiple readers are listening to the same
1627 [e4defrag] donorname=str
1628 File will be used as a block donor(swap extents between files)
1629 [e4defrag] inplace=int
1630 Configure donor file blocks allocation strategy
1631 0(default): Preallocate donor's file on init
1632 1 : allocate space immidietly inside defragment event,
1633 and free right after event
1637 6.0 Interpreting the output
1638 ---------------------------
1640 fio spits out a lot of output. While running, fio will display the
1641 status of the jobs created. An example of that would be:
1643 Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
1645 The characters inside the square brackets denote the current status of
1646 each thread. The possible values (in typical life cycle order) are:
1650 P Thread setup, but not started.
1652 I Thread initialized, waiting or generating necessary data.
1653 p Thread running pre-reading file(s).
1654 R Running, doing sequential reads.
1655 r Running, doing random reads.
1656 W Running, doing sequential writes.
1657 w Running, doing random writes.
1658 M Running, doing mixed sequential reads/writes.
1659 m Running, doing mixed random reads/writes.
1660 F Running, currently waiting for fsync()
1661 f Running, finishing up (writing IO logs, etc)
1662 V Running, doing verification of written data.
1663 E Thread exited, not reaped by main thread yet.
1665 X Thread reaped, exited with an error.
1666 K Thread reaped, exited due to signal.
1668 Fio will condense the thread string as not to take up more space on the
1669 command line as is needed. For instance, if you have 10 readers and 10
1670 writers running, the output would look like this:
1672 Jobs: 20 (f=20): [R(10),W(10)] [4.0% done] [2103MB/0KB/0KB /s] [538K/0/0 iops] [eta 57m:36s]
1674 Fio will still maintain the ordering, though. So the above means that jobs
1675 1..10 are readers, and 11..20 are writers.
1677 The other values are fairly self explanatory - number of threads
1678 currently running and doing io, rate of io since last check (read speed
1679 listed first, then write speed), and the estimated completion percentage
1680 and time for the running group. It's impossible to estimate runtime of
1681 the following groups (if any). Note that the string is displayed in order,
1682 so it's possible to tell which of the jobs are currently doing what. The
1683 first character is the first job defined in the job file, and so forth.
1685 When fio is done (or interrupted by ctrl-c), it will show the data for
1686 each thread, group of threads, and disks in that order. For each data
1687 direction, the output looks like:
1689 Client1 (g=0): err= 0:
1690 write: io= 32MB, bw= 666KB/s, iops=89 , runt= 50320msec
1691 slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92
1692 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82
1693 bw (KB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
1694 cpu : usr=1.49%, sys=0.25%, ctx=7969, majf=0, minf=17
1695 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
1696 submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
1697 complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
1698 issued r/w: total=0/32768, short=0/0
1699 lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
1700 lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%
1702 The client number is printed, along with the group id and error of that
1703 thread. Below is the io statistics, here for writes. In the order listed,
1706 io= Number of megabytes io performed
1707 bw= Average bandwidth rate
1708 iops= Average IOs performed per second
1709 runt= The runtime of that thread
1710 slat= Submission latency (avg being the average, stdev being the
1711 standard deviation). This is the time it took to submit
1712 the io. For sync io, the slat is really the completion
1713 latency, since queue/complete is one operation there. This
1714 value can be in milliseconds or microseconds, fio will choose
1715 the most appropriate base and print that. In the example
1716 above, milliseconds is the best scale. Note: in --minimal mode
1717 latencies are always expressed in microseconds.
1718 clat= Completion latency. Same names as slat, this denotes the
1719 time from submission to completion of the io pieces. For
1720 sync io, clat will usually be equal (or very close) to 0,
1721 as the time from submit to complete is basically just
1722 CPU time (io has already been done, see slat explanation).
1723 bw= Bandwidth. Same names as the xlat stats, but also includes
1724 an approximate percentage of total aggregate bandwidth
1725 this thread received in this group. This last value is
1726 only really useful if the threads in this group are on the
1727 same disk, since they are then competing for disk access.
1728 cpu= CPU usage. User and system time, along with the number
1729 of context switches this thread went through, usage of
1730 system and user time, and finally the number of major
1731 and minor page faults.
1732 IO depths= The distribution of io depths over the job life time. The
1733 numbers are divided into powers of 2, so for example the
1734 16= entries includes depths up to that value but higher
1735 than the previous entry. In other words, it covers the
1736 range from 16 to 31.
1737 IO submit= How many pieces of IO were submitting in a single submit
1738 call. Each entry denotes that amount and below, until
1739 the previous entry - eg, 8=100% mean that we submitted
1740 anywhere in between 5-8 ios per submit call.
1741 IO complete= Like the above submit number, but for completions instead.
1742 IO issued= The number of read/write requests issued, and how many
1744 IO latencies= The distribution of IO completion latencies. This is the
1745 time from when IO leaves fio and when it gets completed.
1746 The numbers follow the same pattern as the IO depths,
1747 meaning that 2=1.6% means that 1.6% of the IO completed
1748 within 2 msecs, 20=12.8% means that 12.8% of the IO
1749 took more than 10 msecs, but less than (or equal to) 20 msecs.
1751 After each client has been listed, the group statistics are printed. They
1752 will look like this:
1754 Run status group 0 (all jobs):
1755 READ: io=64MB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
1756 WRITE: io=64MB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
1758 For each data direction, it prints:
1760 io= Number of megabytes io performed.
1761 aggrb= Aggregate bandwidth of threads in this group.
1762 minb= The minimum average bandwidth a thread saw.
1763 maxb= The maximum average bandwidth a thread saw.
1764 mint= The smallest runtime of the threads in that group.
1765 maxt= The longest runtime of the threads in that group.
1767 And finally, the disk statistics are printed. They will look like this:
1769 Disk stats (read/write):
1770 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
1772 Each value is printed for both reads and writes, with reads first. The
1775 ios= Number of ios performed by all groups.
1776 merge= Number of merges io the io scheduler.
1777 ticks= Number of ticks we kept the disk busy.
1778 io_queue= Total time spent in the disk queue.
1779 util= The disk utilization. A value of 100% means we kept the disk
1780 busy constantly, 50% would be a disk idling half of the time.
1782 It is also possible to get fio to dump the current output while it is
1783 running, without terminating the job. To do that, send fio the USR1 signal.
1784 You can also get regularly timed dumps by using the --status-interval
1785 parameter, or by creating a file in /tmp named fio-dump-status. If fio
1786 sees this file, it will unlink it and dump the current output status.
1792 For scripted usage where you typically want to generate tables or graphs
1793 of the results, fio can output the results in a semicolon separated format.
1794 The format is one long line of values, such as:
1796 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%
1797 A description of this job goes here.
1799 The job description (if provided) follows on a second line.
1801 To enable terse output, use the --minimal command line option. The first
1802 value is the version of the terse output format. If the output has to
1803 be changed for some reason, this number will be incremented by 1 to
1804 signify that change.
1806 Split up, the format is as follows:
1808 terse version, fio version, jobname, groupid, error
1810 Total IO (KB), bandwidth (KB/sec), IOPS, runtime (msec)
1811 Submission latency: min, max, mean, deviation (usec)
1812 Completion latency: min, max, mean, deviation (usec)
1813 Completion latency percentiles: 20 fields (see below)
1814 Total latency: min, max, mean, deviation (usec)
1815 Bw (KB/s): min, max, aggregate percentage of total, mean, deviation
1817 Total IO (KB), bandwidth (KB/sec), IOPS, runtime (msec)
1818 Submission latency: min, max, mean, deviation (usec)
1819 Completion latency: min, max, mean, deviation (usec)
1820 Completion latency percentiles: 20 fields (see below)
1821 Total latency: min, max, mean, deviation (usec)
1822 Bw (KB/s): min, max, aggregate percentage of total, mean, deviation
1823 CPU usage: user, system, context switches, major faults, minor faults
1824 IO depths: <=1, 2, 4, 8, 16, 32, >=64
1825 IO latencies microseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000
1826 IO latencies milliseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, 2000, >=2000
1827 Disk utilization: Disk name, Read ios, write ios,
1828 Read merges, write merges,
1829 Read ticks, write ticks,
1830 Time spent in queue, disk utilization percentage
1831 Additional Info (dependent on continue_on_error, default off): total # errors, first error code
1833 Additional Info (dependent on description being set): Text description
1835 Completion latency percentiles can be a grouping of up to 20 sets, so
1836 for the terse output fio writes all of them. Each field will look like this:
1840 which is the Xth percentile, and the usec latency associated with it.
1842 For disk utilization, all disks used by fio are shown. So for each disk
1843 there will be a disk utilization section.
1846 8.0 Trace file format
1847 ---------------------
1848 There are two trace file format that you can encounter. The older (v1) format
1849 is unsupported since version 1.20-rc3 (March 2008). It will still be described
1850 below in case that you get an old trace and want to understand it.
1852 In any case the trace is a simple text file with a single action per line.
1855 8.1 Trace file format v1
1856 ------------------------
1857 Each line represents a single io action in the following format:
1861 where rw=0/1 for read/write, and the offset and length entries being in bytes.
1863 This format is not supported in Fio versions => 1.20-rc3.
1866 8.2 Trace file format v2
1867 ------------------------
1868 The second version of the trace file format was added in Fio version 1.17.
1869 It allows to access more then one file per trace and has a bigger set of
1870 possible file actions.
1872 The first line of the trace file has to be:
1876 Following this can be lines in two different formats, which are described below.
1878 The file management format:
1882 The filename is given as an absolute path. The action can be one of these:
1884 add Add the given filename to the trace
1885 open Open the file with the given filename. The filename has to have
1886 been added with the add action before.
1887 close Close the file with the given filename. The file has to have been
1891 The file io action format:
1893 filename action offset length
1895 The filename is given as an absolute path, and has to have been added and opened
1896 before it can be used with this format. The offset and length are given in
1897 bytes. The action can be one of these:
1899 wait Wait for 'offset' microseconds. Everything below 100 is discarded.
1900 read Read 'length' bytes beginning from 'offset'
1901 write Write 'length' bytes beginning from 'offset'
1902 sync fsync() the file
1903 datasync fdatasync() the file
1904 trim trim the given file from the given 'offset' for 'length' bytes
1907 9.0 CPU idleness profiling
1908 --------------------------
1909 In some cases, we want to understand CPU overhead in a test. For example,
1910 we test patches for the specific goodness of whether they reduce CPU usage.
1911 fio implements a balloon approach to create a thread per CPU that runs at
1912 idle priority, meaning that it only runs when nobody else needs the cpu.
1913 By measuring the amount of work completed by the thread, idleness of each
1914 CPU can be derived accordingly.
1916 An unit work is defined as touching a full page of unsigned characters. Mean
1917 and standard deviation of time to complete an unit work is reported in "unit
1918 work" section. Options can be chosen to report detailed percpu idleness or
1919 overall system idleness by aggregating percpu stats.
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