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 the 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,
227 int SI integer. A whole number value, which may contain a suffix
228 describing the base of the number. Accepted suffixes are k/m/g/t/p,
229 meaning kilo, mega, giga, tera, and peta. The suffix is not case
230 sensitive, and you may also include trailing 'b' (eg 'kb' is the same
231 as 'k'). So if you want to specify 4096, you could either write
232 out '4096' or just give 4k. The suffixes signify base 2 values, so
233 1024 is 1k and 1024k is 1m and so on, unless the suffix is explicitly
234 set to a base 10 value using 'kib', 'mib', 'gib', etc. If that is the
235 case, then 1000 is used as the multiplier. This can be handy for
236 disks, since manufacturers generally use base 10 values when listing
237 the capacity of a drive. If the option accepts an upper and lower
238 range, use a colon ':' or minus '-' to separate such values. May also
239 include a prefix to indicate numbers base. If 0x is used, the number
240 is assumed to be hexadecimal. See irange.
241 bool Boolean. Usually parsed as an integer, however only defined for
242 true and false (1 and 0).
243 irange Integer range with suffix. Allows value range to be given, such
244 as 1024-4096. A colon may also be used as the separator, eg
245 1k:4k. If the option allows two sets of ranges, they can be
246 specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see
248 float_list A list of floating numbers, separated by a ':' character.
250 With the above in mind, here follows the complete list of fio job
253 name=str ASCII name of the job. This may be used to override the
254 name printed by fio for this job. Otherwise the job
255 name is used. On the command line this parameter has the
256 special purpose of also signaling the start of a new
259 description=str Text description of the job. Doesn't do anything except
260 dump this text description when this job is run. It's
263 directory=str Prefix filenames with this directory. Used to place files
264 in a different location than "./".
266 filename=str Fio normally makes up a filename based on the job name,
267 thread number, and file number. If you want to share
268 files between threads in a job or several jobs, specify
269 a filename for each of them to override the default. If
270 the ioengine used is 'net', the filename is the host, port,
271 and protocol to use in the format of =host,port,protocol.
272 See ioengine=net for more. If the ioengine is file based, you
273 can specify a number of files by separating the names with a
274 ':' colon. So if you wanted a job to open /dev/sda and /dev/sdb
275 as the two working files, you would use
276 filename=/dev/sda:/dev/sdb. On Windows, disk devices are
277 accessed as \\.\PhysicalDrive0 for the first device,
278 \\.\PhysicalDrive1 for the second etc. Note: Windows and
279 FreeBSD prevent write access to areas of the disk containing
280 in-use data (e.g. filesystems).
281 If the wanted filename does need to include a colon, then
282 escape that with a '\' character. For instance, if the filename
283 is "/dev/dsk/foo@3,0:c", then you would use
284 filename="/dev/dsk/foo@3,0\:c". '-' is a reserved name, meaning
285 stdin or stdout. Which of the two depends on the read/write
289 If sharing multiple files between jobs, it is usually necessary
290 to have fio generate the exact names that you want. By default,
291 fio will name a file based on the default file format
292 specification of jobname.jobnumber.filenumber. With this
293 option, that can be customized. Fio will recognize and replace
294 the following keywords in this string:
297 The name of the worker thread or process.
300 The incremental number of the worker thread or
304 The incremental number of the file for that worker
307 To have dependent jobs share a set of files, this option can
308 be set to have fio generate filenames that are shared between
309 the two. For instance, if testfiles.$filenum is specified,
310 file number 4 for any job will be named testfiles.4. The
311 default of $jobname.$jobnum.$filenum will be used if
312 no other format specifier is given.
314 opendir=str Tell fio to recursively add any file it can find in this
315 directory and down the file system tree.
317 lockfile=str Fio defaults to not locking any files before it does
318 IO to them. If a file or file descriptor is shared, fio
319 can serialize IO to that file to make the end result
320 consistent. This is usual for emulating real workloads that
321 share files. The lock modes are:
323 none No locking. The default.
324 exclusive Only one thread/process may do IO,
325 excluding all others.
326 readwrite Read-write locking on the file. Many
327 readers may access the file at the
328 same time, but writes get exclusive
332 rw=str Type of io pattern. Accepted values are:
334 read Sequential reads
335 write Sequential writes
336 randwrite Random writes
337 randread Random reads
338 rw,readwrite Sequential mixed reads and writes
339 randrw Random mixed reads and writes
341 For the mixed io types, the default is to split them 50/50.
342 For certain types of io the result may still be skewed a bit,
343 since the speed may be different. It is possible to specify
344 a number of IO's to do before getting a new offset, this is
345 one by appending a ':<nr>' to the end of the string given.
346 For a random read, it would look like 'rw=randread:8' for
347 passing in an offset modifier with a value of 8. If the
348 suffix is used with a sequential IO pattern, then the value
349 specified will be added to the generated offset for each IO.
350 For instance, using rw=write:4k will skip 4k for every
351 write. It turns sequential IO into sequential IO with holes.
352 See the 'rw_sequencer' option.
354 rw_sequencer=str If an offset modifier is given by appending a number to
355 the rw=<str> line, then this option controls how that
356 number modifies the IO offset being generated. Accepted
359 sequential Generate sequential offset
360 identical Generate the same offset
362 'sequential' is only useful for random IO, where fio would
363 normally generate a new random offset for every IO. If you
364 append eg 8 to randread, you would get a new random offset for
365 every 8 IO's. The result would be a seek for only every 8
366 IO's, instead of for every IO. Use rw=randread:8 to specify
367 that. As sequential IO is already sequential, setting
368 'sequential' for that would not result in any differences.
369 'identical' behaves in a similar fashion, except it sends
370 the same offset 8 number of times before generating a new
373 kb_base=int The base unit for a kilobyte. The defacto base is 2^10, 1024.
374 Storage manufacturers like to use 10^3 or 1000 as a base
375 ten unit instead, for obvious reasons. Allow values are
376 1024 or 1000, with 1024 being the default.
378 unified_rw_reporting=bool Fio normally reports statistics on a per
379 data direction basis, meaning that read, write, and trim are
380 accounted and reported separately. If this option is set,
381 the fio will sum the results and report them as "mixed"
384 randrepeat=bool For random IO workloads, seed the generator in a predictable
385 way so that results are repeatable across repetitions.
387 use_os_rand=bool Fio can either use the random generator supplied by the OS
388 to generator random offsets, or it can use it's own internal
389 generator (based on Tausworthe). Default is to use the
390 internal generator, which is often of better quality and
393 fallocate=str Whether pre-allocation is performed when laying down files.
396 none Do not pre-allocate space
397 posix Pre-allocate via posix_fallocate()
398 keep Pre-allocate via fallocate() with
399 FALLOC_FL_KEEP_SIZE set
400 0 Backward-compatible alias for 'none'
401 1 Backward-compatible alias for 'posix'
403 May not be available on all supported platforms. 'keep' is only
404 available on Linux.If using ZFS on Solaris this must be set to
405 'none' because ZFS doesn't support it. Default: 'posix'.
407 fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
408 on what IO patterns it is likely to issue. Sometimes you
409 want to test specific IO patterns without telling the
410 kernel about it, in which case you can disable this option.
411 If set, fio will use POSIX_FADV_SEQUENTIAL for sequential
412 IO and POSIX_FADV_RANDOM for random IO.
414 size=int The total size of file io for this job. Fio will run until
415 this many bytes has been transferred, unless runtime is
416 limited by other options (such as 'runtime', for instance).
417 Unless specific nrfiles and filesize options are given,
418 fio will divide this size between the available files
419 specified by the job. If not set, fio will use the full
420 size of the given files or devices. If the the files
421 do not exist, size must be given. It is also possible to
422 give size as a percentage between 1 and 100. If size=20%
423 is given, fio will use 20% of the full size of the given
426 filesize=int Individual file sizes. May be a range, in which case fio
427 will select sizes for files at random within the given range
428 and limited to 'size' in total (if that is given). If not
429 given, each created file is the same size.
432 fill_fs=bool Sets size to something really large and waits for ENOSPC (no
433 space left on device) as the terminating condition. Only makes
434 sense with sequential write. For a read workload, the mount
435 point will be filled first then IO started on the result. This
436 option doesn't make sense if operating on a raw device node,
437 since the size of that is already known by the file system.
438 Additionally, writing beyond end-of-device will not return
442 bs=int The block size used for the io units. Defaults to 4k. Values
443 can be given for both read and writes. If a single int is
444 given, it will apply to both. If a second int is specified
445 after a comma, it will apply to writes only. In other words,
446 the format is either bs=read_and_write or bs=read,write.
447 bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
448 for writes. If you only wish to set the write size, you
449 can do so by passing an empty read size - bs=,8k will set
450 8k for writes and leave the read default value.
453 ba=int At what boundary to align random IO offsets. Defaults to
454 the same as 'blocksize' the minimum blocksize given.
455 Minimum alignment is typically 512b for using direct IO,
456 though it usually depends on the hardware block size. This
457 option is mutually exclusive with using a random map for
458 files, so it will turn off that option.
460 blocksize_range=irange
461 bsrange=irange Instead of giving a single block size, specify a range
462 and fio will mix the issued io block sizes. The issued
463 io unit will always be a multiple of the minimum value
464 given (also see bs_unaligned). Applies to both reads and
465 writes, however a second range can be given after a comma.
468 bssplit=str Sometimes you want even finer grained control of the
469 block sizes issued, not just an even split between them.
470 This option allows you to weight various block sizes,
471 so that you are able to define a specific amount of
472 block sizes issued. The format for this option is:
474 bssplit=blocksize/percentage:blocksize/percentage
476 for as many block sizes as needed. So if you want to define
477 a workload that has 50% 64k blocks, 10% 4k blocks, and
478 40% 32k blocks, you would write:
480 bssplit=4k/10:64k/50:32k/40
482 Ordering does not matter. If the percentage is left blank,
483 fio will fill in the remaining values evenly. So a bssplit
484 option like this one:
486 bssplit=4k/50:1k/:32k/
488 would have 50% 4k ios, and 25% 1k and 32k ios. The percentages
489 always add up to 100, if bssplit is given a range that adds
490 up to more, it will error out.
492 bssplit also supports giving separate splits to reads and
493 writes. The format is identical to what bs= accepts. You
494 have to separate the read and write parts with a comma. So
495 if you want a workload that has 50% 2k reads and 50% 4k reads,
496 while having 90% 4k writes and 10% 8k writes, you would
499 bssplit=2k/50:4k/50,4k/90,8k/10
502 bs_unaligned If this option is given, any byte size value within bsrange
503 may be used as a block range. This typically wont work with
504 direct IO, as that normally requires sector alignment.
506 zero_buffers If this option is given, fio will init the IO buffers to
507 all zeroes. The default is to fill them with random data.
509 refill_buffers If this option is given, fio will refill the IO buffers
510 on every submit. The default is to only fill it at init
511 time and reuse that data. Only makes sense if zero_buffers
512 isn't specified, naturally. If data verification is enabled,
513 refill_buffers is also automatically enabled.
515 scramble_buffers=bool If refill_buffers is too costly and the target is
516 using data deduplication, then setting this option will
517 slightly modify the IO buffer contents to defeat normal
518 de-dupe attempts. This is not enough to defeat more clever
519 block compression attempts, but it will stop naive dedupe of
520 blocks. Default: true.
522 buffer_compress_percentage=int If this is set, then fio will attempt to
523 provide IO buffer content (on WRITEs) that compress to
524 the specified level. Fio does this by providing a mix of
525 random data and zeroes. Note that this is per block size
526 unit, for file/disk wide compression level that matches
527 this setting, you'll also want to set refill_buffers.
529 buffer_compress_chunk=int See buffer_compress_percentage. This
530 setting allows fio to manage how big the ranges of random
531 data and zeroed data is. Without this set, fio will
532 provide buffer_compress_percentage of blocksize random
533 data, followed by the remaining zeroed. With this set
534 to some chunk size smaller than the block size, fio can
535 alternate random and zeroed data throughout the IO
538 nrfiles=int Number of files to use for this job. Defaults to 1.
540 openfiles=int Number of files to keep open at the same time. Defaults to
541 the same as nrfiles, can be set smaller to limit the number
544 file_service_type=str Defines how fio decides which file from a job to
545 service next. The following types are defined:
547 random Just choose a file at random.
549 roundrobin Round robin over open files. This
552 sequential Finish one file before moving on to
553 the next. Multiple files can still be
554 open depending on 'openfiles'.
556 The string can have a number appended, indicating how
557 often to switch to a new file. So if option random:4 is
558 given, fio will switch to a new random file after 4 ios
561 ioengine=str Defines how the job issues io to the file. The following
564 sync Basic read(2) or write(2) io. lseek(2) is
565 used to position the io location.
567 psync Basic pread(2) or pwrite(2) io.
569 vsync Basic readv(2) or writev(2) IO.
571 libaio Linux native asynchronous io. Note that Linux
572 may only support queued behaviour with
573 non-buffered IO (set direct=1 or buffered=0).
574 This engine defines engine specific options.
576 posixaio glibc posix asynchronous io.
578 solarisaio Solaris native asynchronous io.
580 windowsaio Windows native asynchronous io.
582 mmap File is memory mapped and data copied
583 to/from using memcpy(3).
585 splice splice(2) is used to transfer the data and
586 vmsplice(2) to transfer data from user
589 syslet-rw Use the syslet system calls to make
590 regular read/write async.
592 sg SCSI generic sg v3 io. May either be
593 synchronous using the SG_IO ioctl, or if
594 the target is an sg character device
595 we use read(2) and write(2) for asynchronous
598 null Doesn't transfer any data, just pretends
599 to. This is mainly used to exercise fio
600 itself and for debugging/testing purposes.
602 net Transfer over the network to given host:port.
603 Depending on the protocol used, the hostname,
604 port, listen and filename options are used to
605 specify what sort of connection to make, while
606 the protocol option determines which protocol
608 This engine defines engine specific options.
610 netsplice Like net, but uses splice/vmsplice to
611 map data and send/receive.
612 This engine defines engine specific options.
614 cpuio Doesn't transfer any data, but burns CPU
615 cycles according to the cpuload= and
616 cpucycle= options. Setting cpuload=85
617 will cause that job to do nothing but burn
618 85% of the CPU. In case of SMP machines,
619 use numjobs=<no_of_cpu> to get desired CPU
620 usage, as the cpuload only loads a single
621 CPU at the desired rate.
623 guasi The GUASI IO engine is the Generic Userspace
624 Asyncronous Syscall Interface approach
627 http://www.xmailserver.org/guasi-lib.html
629 for more info on GUASI.
631 rdma The RDMA I/O engine supports both RDMA
632 memory semantics (RDMA_WRITE/RDMA_READ) and
633 channel semantics (Send/Recv) for the
634 InfiniBand, RoCE and iWARP protocols.
636 falloc IO engine that does regular fallocate to
637 simulate data transfer as fio ioengine.
638 DDIR_READ does fallocate(,mode = keep_size,)
639 DDIR_WRITE does fallocate(,mode = 0)
640 DDIR_TRIM does fallocate(,mode = punch_hole)
642 e4defrag IO engine that does regular EXT4_IOC_MOVE_EXT
643 ioctls to simulate defragment activity in
644 request to DDIR_WRITE event
646 external Prefix to specify loading an external
647 IO engine object file. Append the engine
648 filename, eg ioengine=external:/tmp/foo.o
649 to load ioengine foo.o in /tmp.
651 iodepth=int This defines how many io units to keep in flight against
652 the file. The default is 1 for each file defined in this
653 job, can be overridden with a larger value for higher
654 concurrency. Note that increasing iodepth beyond 1 will not
655 affect synchronous ioengines (except for small degress when
656 verify_async is in use). Even async engines may impose OS
657 restrictions causing the desired depth not to be achieved.
658 This may happen on Linux when using libaio and not setting
659 direct=1, since buffered IO is not async on that OS. Keep an
660 eye on the IO depth distribution in the fio output to verify
661 that the achieved depth is as expected. Default: 1.
663 iodepth_batch_submit=int
664 iodepth_batch=int This defines how many pieces of IO to submit at once.
665 It defaults to 1 which means that we submit each IO
666 as soon as it is available, but can be raised to submit
667 bigger batches of IO at the time.
669 iodepth_batch_complete=int This defines how many pieces of IO to retrieve
670 at once. It defaults to 1 which means that we'll ask
671 for a minimum of 1 IO in the retrieval process from
672 the kernel. The IO retrieval will go on until we
673 hit the limit set by iodepth_low. If this variable is
674 set to 0, then fio will always check for completed
675 events before queuing more IO. This helps reduce
676 IO latency, at the cost of more retrieval system calls.
678 iodepth_low=int The low water mark indicating when to start filling
679 the queue again. Defaults to the same as iodepth, meaning
680 that fio will attempt to keep the queue full at all times.
681 If iodepth is set to eg 16 and iodepth_low is set to 4, then
682 after fio has filled the queue of 16 requests, it will let
683 the depth drain down to 4 before starting to fill it again.
685 direct=bool If value is true, use non-buffered io. This is usually
686 O_DIRECT. Note that ZFS on Solaris doesn't support direct io.
687 On Windows the synchronous ioengines don't support direct io.
689 buffered=bool If value is true, use buffered io. This is the opposite
690 of the 'direct' option. Defaults to true.
692 offset=int Start io at the given offset in the file. The data before
693 the given offset will not be touched. This effectively
694 caps the file size at real_size - offset.
696 offset_increment=int If this is provided, then the real offset becomes
697 the offset + offset_increment * thread_number, where the
698 thread number is a counter that starts at 0 and is incremented
699 for each job. This option is useful if there are several jobs
700 which are intended to operate on a file in parallel in disjoint
701 segments, with even spacing between the starting points.
703 fsync=int If writing to a file, issue a sync of the dirty data
704 for every number of blocks given. For example, if you give
705 32 as a parameter, fio will sync the file for every 32
706 writes issued. If fio is using non-buffered io, we may
707 not sync the file. The exception is the sg io engine, which
708 synchronizes the disk cache anyway.
710 fdatasync=int Like fsync= but uses fdatasync() to only sync data and not
712 In FreeBSD and Windows there is no fdatasync(), this falls back to
715 sync_file_range=str:val Use sync_file_range() for every 'val' number of
716 write operations. Fio will track range of writes that
717 have happened since the last sync_file_range() call. 'str'
718 can currently be one or more of:
720 wait_before SYNC_FILE_RANGE_WAIT_BEFORE
721 write SYNC_FILE_RANGE_WRITE
722 wait_after SYNC_FILE_RANGE_WAIT_AFTER
724 So if you do sync_file_range=wait_before,write:8, fio would
725 use SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE for
726 every 8 writes. Also see the sync_file_range(2) man page.
727 This option is Linux specific.
729 overwrite=bool If true, writes to a file will always overwrite existing
730 data. If the file doesn't already exist, it will be
731 created before the write phase begins. If the file exists
732 and is large enough for the specified write phase, nothing
735 end_fsync=bool If true, fsync file contents when a write stage has completed.
737 fsync_on_close=bool If true, fio will fsync() a dirty file on close.
738 This differs from end_fsync in that it will happen on every
739 file close, not just at the end of the job.
741 rwmixread=int How large a percentage of the mix should be reads.
743 rwmixwrite=int How large a percentage of the mix should be writes. If both
744 rwmixread and rwmixwrite is given and the values do not add
745 up to 100%, the latter of the two will be used to override
746 the first. This may interfere with a given rate setting,
747 if fio is asked to limit reads or writes to a certain rate.
748 If that is the case, then the distribution may be skewed.
750 random_distribution=str:float By default, fio will use a completely uniform
751 random distribution when asked to perform random IO. Sometimes
752 it is useful to skew the distribution in specific ways,
753 ensuring that some parts of the data is more hot than others.
754 fio includes the following distribution models:
756 random Uniform random distribution
757 zipf Zipf distribution
758 pareto Pareto distribution
760 When using a zipf or pareto distribution, an input value
761 is also needed to define the access pattern. For zipf, this
762 is the zipf theta. For pareto, it's the pareto power. Fio
763 includes a test program, genzipf, that can be used visualize
764 what the given input values will yield in terms of hit rates.
765 If you wanted to use zipf with a theta of 1.2, you would use
766 random_distribution=zipf:1.2 as the option. If a non-uniform
767 model is used, fio will disable use of the random map.
769 norandommap Normally fio will cover every block of the file when doing
770 random IO. If this option is given, fio will just get a
771 new random offset without looking at past io history. This
772 means that some blocks may not be read or written, and that
773 some blocks may be read/written more than once. This option
774 is mutually exclusive with verify= if and only if multiple
775 blocksizes (via bsrange=) are used, since fio only tracks
776 complete rewrites of blocks.
778 softrandommap=bool See norandommap. If fio runs with the random block map
779 enabled and it fails to allocate the map, if this option is
780 set it will continue without a random block map. As coverage
781 will not be as complete as with random maps, this option is
784 random_generator=str Fio supports the following engines for generating
785 IO offsets for random IO:
787 tausworthe Strong 2^88 cycle random number generator
788 lfsr Linear feedback shift register generator
790 Tausworthe is a strong random number generator, but it
791 requires tracking on the side if we want to ensure that
792 blocks are only read or written once. LFSR guarantees
793 that we never generate the same offset twice, and it's
794 also less computationally expensive. It's not a true
795 random generator, however, though for IO purposes it's
796 typically good enough. LFSR only works with single
797 block sizes, not with workloads that use multiple block
798 sizes. If used with such a workload, fio may read or write
799 some blocks multiple times.
801 nice=int Run the job with the given nice value. See man nice(2).
803 prio=int Set the io priority value of this job. Linux limits us to
804 a positive value between 0 and 7, with 0 being the highest.
807 prioclass=int Set the io priority class. See man ionice(1).
809 thinktime=int Stall the job x microseconds after an io has completed before
810 issuing the next. May be used to simulate processing being
811 done by an application. See thinktime_blocks and
815 Only valid if thinktime is set - pretend to spend CPU time
816 doing something with the data received, before falling back
817 to sleeping for the rest of the period specified by
821 Only valid if thinktime is set - control how many blocks
822 to issue, before waiting 'thinktime' usecs. If not set,
823 defaults to 1 which will make fio wait 'thinktime' usecs
826 rate=int Cap the bandwidth used by this job. The number is in bytes/sec,
827 the normal suffix rules apply. You can use rate=500k to limit
828 reads and writes to 500k each, or you can specify read and
829 writes separately. Using rate=1m,500k would limit reads to
830 1MB/sec and writes to 500KB/sec. Capping only reads or
831 writes can be done with rate=,500k or rate=500k,. The former
832 will only limit writes (to 500KB/sec), the latter will only
835 ratemin=int Tell fio to do whatever it can to maintain at least this
836 bandwidth. Failing to meet this requirement, will cause
837 the job to exit. The same format as rate is used for
838 read vs write separation.
840 rate_iops=int Cap the bandwidth to this number of IOPS. Basically the same
841 as rate, just specified independently of bandwidth. If the
842 job is given a block size range instead of a fixed value,
843 the smallest block size is used as the metric. The same format
844 as rate is used for read vs write seperation.
846 rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
847 the job to exit. The same format as rate is used for read vs
850 max_latency=int If set, fio will exit the job if it exceeds this maximum
851 latency. It will exit with an ETIME error.
853 ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
856 cpumask=int Set the CPU affinity of this job. The parameter given is a
857 bitmask of allowed CPU's the job may run on. So if you want
858 the allowed CPUs to be 1 and 5, you would pass the decimal
859 value of (1 << 1 | 1 << 5), or 34. See man
860 sched_setaffinity(2). This may not work on all supported
861 operating systems or kernel versions. This option doesn't
862 work well for a higher CPU count than what you can store in
863 an integer mask, so it can only control cpus 1-32. For
864 boxes with larger CPU counts, use cpus_allowed.
866 cpus_allowed=str Controls the same options as cpumask, but it allows a text
867 setting of the permitted CPUs instead. So to use CPUs 1 and
868 5, you would specify cpus_allowed=1,5. This options also
869 allows a range of CPUs. Say you wanted a binding to CPUs
870 1, 5, and 8-15, you would set cpus_allowed=1,5,8-15.
872 numa_cpu_nodes=str Set this job running on spcified NUMA nodes' CPUs. The
873 arguments allow comma delimited list of cpu numbers,
874 A-B ranges, or 'all'. Note, to enable numa options support,
875 fio must be built on a system with libnuma-dev(el) installed.
877 numa_mem_policy=str Set this job's memory policy and corresponding NUMA
878 nodes. Format of the argements:
880 `mode' is one of the following memory policy:
881 default, prefer, bind, interleave, local
882 For `default' and `local' memory policy, no node is
883 needed to be specified.
884 For `prefer', only one node is allowed.
885 For `bind' and `interleave', it allow comma delimited
886 list of numbers, A-B ranges, or 'all'.
888 startdelay=time Start this job the specified number of seconds after fio
889 has started. Only useful if the job file contains several
890 jobs, and you want to delay starting some jobs to a certain
893 runtime=time Tell fio to terminate processing after the specified number
894 of seconds. It can be quite hard to determine for how long
895 a specified job will run, so this parameter is handy to
896 cap the total runtime to a given time.
898 time_based If set, fio will run for the duration of the runtime
899 specified even if the file(s) are completely read or
900 written. It will simply loop over the same workload
901 as many times as the runtime allows.
903 ramp_time=time If set, fio will run the specified workload for this amount
904 of time before logging any performance numbers. Useful for
905 letting performance settle before logging results, thus
906 minimizing the runtime required for stable results. Note
907 that the ramp_time is considered lead in time for a job,
908 thus it will increase the total runtime if a special timeout
909 or runtime is specified.
911 invalidate=bool Invalidate the buffer/page cache parts for this file prior
912 to starting io. Defaults to true.
914 sync=bool Use sync io for buffered writes. For the majority of the
915 io engines, this means using O_SYNC.
918 mem=str Fio can use various types of memory as the io unit buffer.
919 The allowed values are:
921 malloc Use memory from malloc(3) as the buffers.
923 shm Use shared memory as the buffers. Allocated
926 shmhuge Same as shm, but use huge pages as backing.
928 mmap Use mmap to allocate buffers. May either be
929 anonymous memory, or can be file backed if
930 a filename is given after the option. The
931 format is mem=mmap:/path/to/file.
933 mmaphuge Use a memory mapped huge file as the buffer
934 backing. Append filename after mmaphuge, ala
935 mem=mmaphuge:/hugetlbfs/file
937 The area allocated is a function of the maximum allowed
938 bs size for the job, multiplied by the io depth given. Note
939 that for shmhuge and mmaphuge to work, the system must have
940 free huge pages allocated. This can normally be checked
941 and set by reading/writing /proc/sys/vm/nr_hugepages on a
942 Linux system. Fio assumes a huge page is 4MB in size. So
943 to calculate the number of huge pages you need for a given
944 job file, add up the io depth of all jobs (normally one unless
945 iodepth= is used) and multiply by the maximum bs set. Then
946 divide that number by the huge page size. You can see the
947 size of the huge pages in /proc/meminfo. If no huge pages
948 are allocated by having a non-zero number in nr_hugepages,
949 using mmaphuge or shmhuge will fail. Also see hugepage-size.
951 mmaphuge also needs to have hugetlbfs mounted and the file
952 location should point there. So if it's mounted in /huge,
953 you would use mem=mmaphuge:/huge/somefile.
955 iomem_align=int This indiciates the memory alignment of the IO memory buffers.
956 Note that the given alignment is applied to the first IO unit
957 buffer, if using iodepth the alignment of the following buffers
958 are given by the bs used. In other words, if using a bs that is
959 a multiple of the page sized in the system, all buffers will
960 be aligned to this value. If using a bs that is not page
961 aligned, the alignment of subsequent IO memory buffers is the
962 sum of the iomem_align and bs used.
965 Defines the size of a huge page. Must at least be equal
966 to the system setting, see /proc/meminfo. Defaults to 4MB.
967 Should probably always be a multiple of megabytes, so using
968 hugepage-size=Xm is the preferred way to set this to avoid
969 setting a non-pow-2 bad value.
971 exitall When one job finishes, terminate the rest. The default is
972 to wait for each job to finish, sometimes that is not the
975 bwavgtime=int Average the calculated bandwidth over the given time. Value
976 is specified in milliseconds.
978 iopsavgtime=int Average the calculated IOPS over the given time. Value
979 is specified in milliseconds.
981 create_serialize=bool If true, serialize the file creating for the jobs.
982 This may be handy to avoid interleaving of data
983 files, which may greatly depend on the filesystem
984 used and even the number of processors in the system.
986 create_fsync=bool fsync the data file after creation. This is the
989 create_on_open=bool Don't pre-setup the files for IO, just create open()
990 when it's time to do IO to that file.
992 create_only=bool If true, fio will only run the setup phase of the job.
993 If files need to be laid out or updated on disk, only
994 that will be done. The actual job contents are not
997 pre_read=bool If this is given, files will be pre-read into memory before
998 starting the given IO operation. This will also clear
999 the 'invalidate' flag, since it is pointless to pre-read
1000 and then drop the cache. This will only work for IO engines
1001 that are seekable, since they allow you to read the same data
1002 multiple times. Thus it will not work on eg network or splice
1005 unlink=bool Unlink the job files when done. Not the default, as repeated
1006 runs of that job would then waste time recreating the file
1007 set again and again.
1009 loops=int Run the specified number of iterations of this job. Used
1010 to repeat the same workload a given number of times. Defaults
1013 do_verify=bool Run the verify phase after a write phase. Only makes sense if
1014 verify is set. Defaults to 1.
1016 verify=str If writing to a file, fio can verify the file contents
1017 after each iteration of the job. The allowed values are:
1019 md5 Use an md5 sum of the data area and store
1020 it in the header of each block.
1022 crc64 Use an experimental crc64 sum of the data
1023 area and store it in the header of each
1026 crc32c Use a crc32c sum of the data area and store
1027 it in the header of each block.
1029 crc32c-intel Use hardware assisted crc32c calcuation
1030 provided on SSE4.2 enabled processors. Falls
1031 back to regular software crc32c, if not
1032 supported by the system.
1034 crc32 Use a crc32 sum of the data area and store
1035 it in the header of each block.
1037 crc16 Use a crc16 sum of the data area and store
1038 it in the header of each block.
1040 crc7 Use a crc7 sum of the data area and store
1041 it in the header of each block.
1043 sha512 Use sha512 as the checksum function.
1045 sha256 Use sha256 as the checksum function.
1047 sha1 Use optimized sha1 as the checksum function.
1049 meta Write extra information about each io
1050 (timestamp, block number etc.). The block
1051 number is verified. See also verify_pattern.
1053 null Only pretend to verify. Useful for testing
1054 internals with ioengine=null, not for much
1057 This option can be used for repeated burn-in tests of a
1058 system to make sure that the written data is also
1059 correctly read back. If the data direction given is
1060 a read or random read, fio will assume that it should
1061 verify a previously written file. If the data direction
1062 includes any form of write, the verify will be of the
1065 verifysort=bool If set, fio will sort written verify blocks when it deems
1066 it faster to read them back in a sorted manner. This is
1067 often the case when overwriting an existing file, since
1068 the blocks are already laid out in the file system. You
1069 can ignore this option unless doing huge amounts of really
1070 fast IO where the red-black tree sorting CPU time becomes
1073 verify_offset=int Swap the verification header with data somewhere else
1074 in the block before writing. Its swapped back before
1077 verify_interval=int Write the verification header at a finer granularity
1078 than the blocksize. It will be written for chunks the
1079 size of header_interval. blocksize should divide this
1082 verify_pattern=str If set, fio will fill the io buffers with this
1083 pattern. Fio defaults to filling with totally random
1084 bytes, but sometimes it's interesting to fill with a known
1085 pattern for io verification purposes. Depending on the
1086 width of the pattern, fio will fill 1/2/3/4 bytes of the
1087 buffer at the time(it can be either a decimal or a hex number).
1088 The verify_pattern if larger than a 32-bit quantity has to
1089 be a hex number that starts with either "0x" or "0X". Use
1092 verify_fatal=bool Normally fio will keep checking the entire contents
1093 before quitting on a block verification failure. If this
1094 option is set, fio will exit the job on the first observed
1097 verify_dump=bool If set, dump the contents of both the original data
1098 block and the data block we read off disk to files. This
1099 allows later analysis to inspect just what kind of data
1100 corruption occurred. Off by default.
1102 verify_async=int Fio will normally verify IO inline from the submitting
1103 thread. This option takes an integer describing how many
1104 async offload threads to create for IO verification instead,
1105 causing fio to offload the duty of verifying IO contents
1106 to one or more separate threads. If using this offload
1107 option, even sync IO engines can benefit from using an
1108 iodepth setting higher than 1, as it allows them to have
1109 IO in flight while verifies are running.
1111 verify_async_cpus=str Tell fio to set the given CPU affinity on the
1112 async IO verification threads. See cpus_allowed for the
1115 verify_backlog=int Fio will normally verify the written contents of a
1116 job that utilizes verify once that job has completed. In
1117 other words, everything is written then everything is read
1118 back and verified. You may want to verify continually
1119 instead for a variety of reasons. Fio stores the meta data
1120 associated with an IO block in memory, so for large
1121 verify workloads, quite a bit of memory would be used up
1122 holding this meta data. If this option is enabled, fio
1123 will write only N blocks before verifying these blocks.
1125 will verify the previously written blocks before continuing
1128 verify_backlog_batch=int Control how many blocks fio will verify
1129 if verify_backlog is set. If not set, will default to
1130 the value of verify_backlog (meaning the entire queue
1131 is read back and verified). If verify_backlog_batch is
1132 less than verify_backlog then not all blocks will be verified,
1133 if verify_backlog_batch is larger than verify_backlog, some
1134 blocks will be verified more than once.
1137 wait_for_previous Wait for preceeding jobs in the job file to exit, before
1138 starting this one. Can be used to insert serialization
1139 points in the job file. A stone wall also implies starting
1140 a new reporting group.
1142 new_group Start a new reporting group. See: group_reporting.
1144 numjobs=int Create the specified number of clones of this job. May be
1145 used to setup a larger number of threads/processes doing
1146 the same thing. Each thread is reported separately; to see
1147 statistics for all clones as a whole, use group_reporting in
1148 conjunction with new_group.
1150 group_reporting It may sometimes be interesting to display statistics for
1151 groups of jobs as a whole instead of for each individual job.
1152 This is especially true if 'numjobs' is used; looking at
1153 individual thread/process output quickly becomes unwieldy.
1154 To see the final report per-group instead of per-job, use
1155 'group_reporting'. Jobs in a file will be part of the same
1156 reporting group, unless if separated by a stonewall, or by
1159 thread fio defaults to forking jobs, however if this option is
1160 given, fio will use pthread_create(3) to create threads
1163 zonesize=int Divide a file into zones of the specified size. See zoneskip.
1165 zoneskip=int Skip the specified number of bytes when zonesize data has
1166 been read. The two zone options can be used to only do
1167 io on zones of a file.
1169 write_iolog=str Write the issued io patterns to the specified file. See
1170 read_iolog. Specify a separate file for each job, otherwise
1171 the iologs will be interspersed and the file may be corrupt.
1173 read_iolog=str Open an iolog with the specified file name and replay the
1174 io patterns it contains. This can be used to store a
1175 workload and replay it sometime later. The iolog given
1176 may also be a blktrace binary file, which allows fio
1177 to replay a workload captured by blktrace. See blktrace
1178 for how to capture such logging data. For blktrace replay,
1179 the file needs to be turned into a blkparse binary data
1180 file first (blkparse <device> -o /dev/null -d file_for_fio.bin).
1182 replay_no_stall=int When replaying I/O with read_iolog the default behavior
1183 is to attempt to respect the time stamps within the log and
1184 replay them with the appropriate delay between IOPS. By
1185 setting this variable fio will not respect the timestamps and
1186 attempt to replay them as fast as possible while still
1187 respecting ordering. The result is the same I/O pattern to a
1188 given device, but different timings.
1190 replay_redirect=str While replaying I/O patterns using read_iolog the
1191 default behavior is to replay the IOPS onto the major/minor
1192 device that each IOP was recorded from. This is sometimes
1193 undesireable because on a different machine those major/minor
1194 numbers can map to a different device. Changing hardware on
1195 the same system can also result in a different major/minor
1196 mapping. Replay_redirect causes all IOPS to be replayed onto
1197 the single specified device regardless of the device it was
1198 recorded from. i.e. replay_redirect=/dev/sdc would cause all
1199 IO in the blktrace to be replayed onto /dev/sdc. This means
1200 multiple devices will be replayed onto a single, if the trace
1201 contains multiple devices. If you want multiple devices to be
1202 replayed concurrently to multiple redirected devices you must
1203 blkparse your trace into separate traces and replay them with
1204 independent fio invocations. Unfortuantely this also breaks
1205 the strict time ordering between multiple device accesses.
1207 write_bw_log=str If given, write a bandwidth log of the jobs in this job
1208 file. Can be used to store data of the bandwidth of the
1209 jobs in their lifetime. The included fio_generate_plots
1210 script uses gnuplot to turn these text files into nice
1211 graphs. See write_lat_log for behaviour of given
1212 filename. For this option, the suffix is _bw.log.
1214 write_lat_log=str Same as write_bw_log, except that this option stores io
1215 submission, completion, and total latencies instead. If no
1216 filename is given with this option, the default filename of
1217 "jobname_type.log" is used. Even if the filename is given,
1218 fio will still append the type of log. So if one specifies
1222 The actual log names will be foo_slat.log, foo_slat.log,
1223 and foo_lat.log. This helps fio_generate_plot fine the logs
1226 write_bw_log=str If given, write an IOPS log of the jobs in this job
1227 file. See write_bw_log.
1229 write_iops_log=str Same as write_bw_log, but writes IOPS. If no filename is
1230 given with this option, the default filename of
1231 "jobname_type.log" is used. Even if the filename is given,
1232 fio will still append the type of log.
1234 log_avg_msec=int By default, fio will log an entry in the iops, latency,
1235 or bw log for every IO that completes. When writing to the
1236 disk log, that can quickly grow to a very large size. Setting
1237 this option makes fio average the each log entry over the
1238 specified period of time, reducing the resolution of the log.
1241 lockmem=int Pin down the specified amount of memory with mlock(2). Can
1242 potentially be used instead of removing memory or booting
1243 with less memory to simulate a smaller amount of memory.
1245 exec_prerun=str Before running this job, issue the command specified
1248 exec_postrun=str After the job completes, issue the command specified
1251 ioscheduler=str Attempt to switch the device hosting the file to the specified
1252 io scheduler before running.
1254 cpuload=int If the job is a CPU cycle eater, attempt to use the specified
1255 percentage of CPU cycles.
1257 cpuchunks=int If the job is a CPU cycle eater, split the load into
1258 cycles of the given time. In microseconds.
1260 disk_util=bool Generate disk utilization statistics, if the platform
1261 supports it. Defaults to on.
1263 disable_lat=bool Disable measurements of total latency numbers. Useful
1264 only for cutting back the number of calls to gettimeofday,
1265 as that does impact performance at really high IOPS rates.
1266 Note that to really get rid of a large amount of these
1267 calls, this option must be used with disable_slat and
1270 disable_clat=bool Disable measurements of completion latency numbers. See
1273 disable_slat=bool Disable measurements of submission latency numbers. See
1276 disable_bw=bool Disable measurements of throughput/bandwidth numbers. See
1279 clat_percentiles=bool Enable the reporting of percentiles of
1280 completion latencies.
1282 percentile_list=float_list Overwrite the default list of percentiles
1283 for completion latencies. Each number is a floating
1284 number in the range (0,100], and the maximum length of
1285 the list is 20. Use ':' to separate the numbers, and
1286 list the numbers in ascending order. For example,
1287 --percentile_list=99.5:99.9 will cause fio to report
1288 the values of completion latency below which 99.5% and
1289 99.9% of the observed latencies fell, respectively.
1291 clocksource=str Use the given clocksource as the base of timing. The
1292 supported options are:
1294 gettimeofday gettimeofday(2)
1296 clock_gettime clock_gettime(2)
1298 cpu Internal CPU clock source
1300 cpu is the preferred clocksource if it is reliable, as it
1301 is very fast (and fio is heavy on time calls). Fio will
1302 automatically use this clocksource if it's supported and
1303 considered reliable on the system it is running on, unless
1304 another clocksource is specifically set. For x86/x86-64 CPUs,
1305 this means supporting TSC Invariant.
1307 gtod_reduce=bool Enable all of the gettimeofday() reducing options
1308 (disable_clat, disable_slat, disable_bw) plus reduce
1309 precision of the timeout somewhat to really shrink
1310 the gettimeofday() call count. With this option enabled,
1311 we only do about 0.4% of the gtod() calls we would have
1312 done if all time keeping was enabled.
1314 gtod_cpu=int Sometimes it's cheaper to dedicate a single thread of
1315 execution to just getting the current time. Fio (and
1316 databases, for instance) are very intensive on gettimeofday()
1317 calls. With this option, you can set one CPU aside for
1318 doing nothing but logging current time to a shared memory
1319 location. Then the other threads/processes that run IO
1320 workloads need only copy that segment, instead of entering
1321 the kernel with a gettimeofday() call. The CPU set aside
1322 for doing these time calls will be excluded from other
1323 uses. Fio will manually clear it from the CPU mask of other
1326 continue_on_error=str Normally fio will exit the job on the first observed
1327 failure. If this option is set, fio will continue the job when
1328 there is a 'non-fatal error' (EIO or EILSEQ) until the runtime
1329 is exceeded or the I/O size specified is completed. If this
1330 option is used, there are two more stats that are appended,
1331 the total error count and the first error. The error field
1332 given in the stats is the first error that was hit during the
1335 The allowed values are:
1337 none Exit on any IO or verify errors.
1339 read Continue on read errors, exit on all others.
1341 write Continue on write errors, exit on all others.
1343 io Continue on any IO error, exit on all others.
1345 verify Continue on verify errors, exit on all others.
1347 all Continue on all errors.
1349 0 Backward-compatible alias for 'none'.
1351 1 Backward-compatible alias for 'all'.
1353 ignore_error=str Sometimes you want to ignore some errors during test
1354 in that case you can specify error list for each error type.
1355 ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST
1356 errors for given error type is separated with ':'. Error
1357 may be symbol ('ENOSPC', 'ENOMEM') or integer.
1359 ignore_error=EAGAIN,ENOSPC:122
1360 This option will ignore EAGAIN from READ, and ENOSPC and
1361 122(EDQUOT) from WRITE.
1363 error_dump=bool If set dump every error even if it is non fatal, true
1364 by default. If disabled only fatal error will be dumped
1366 cgroup=str Add job to this control group. If it doesn't exist, it will
1367 be created. The system must have a mounted cgroup blkio
1368 mount point for this to work. If your system doesn't have it
1369 mounted, you can do so with:
1371 # mount -t cgroup -o blkio none /cgroup
1373 cgroup_weight=int Set the weight of the cgroup to this value. See
1374 the documentation that comes with the kernel, allowed values
1375 are in the range of 100..1000.
1377 cgroup_nodelete=bool Normally fio will delete the cgroups it has created after
1378 the job completion. To override this behavior and to leave
1379 cgroups around after the job completion, set cgroup_nodelete=1.
1380 This can be useful if one wants to inspect various cgroup
1381 files after job completion. Default: false
1383 uid=int Instead of running as the invoking user, set the user ID to
1384 this value before the thread/process does any work.
1386 gid=int Set group ID, see uid.
1388 flow_id=int The ID of the flow. If not specified, it defaults to being a
1389 global flow. See flow.
1391 flow=int Weight in token-based flow control. If this value is used, then
1392 there is a 'flow counter' which is used to regulate the
1393 proportion of activity between two or more jobs. fio attempts
1394 to keep this flow counter near zero. The 'flow' parameter
1395 stands for how much should be added or subtracted to the flow
1396 counter on each iteration of the main I/O loop. That is, if
1397 one job has flow=8 and another job has flow=-1, then there
1398 will be a roughly 1:8 ratio in how much one runs vs the other.
1400 flow_watermark=int The maximum value that the absolute value of the flow
1401 counter is allowed to reach before the job must wait for a
1402 lower value of the counter.
1404 flow_sleep=int The period of time, in microseconds, to wait after the flow
1405 watermark has been exceeded before retrying operations
1407 In addition, there are some parameters which are only valid when a specific
1408 ioengine is in use. These are used identically to normal parameters, with the
1409 caveat that when used on the command line, they must come after the ioengine
1410 that defines them is selected.
1412 [libaio] userspace_reap Normally, with the libaio engine in use, fio will use
1413 the io_getevents system call to reap newly returned events.
1414 With this flag turned on, the AIO ring will be read directly
1415 from user-space to reap events. The reaping mode is only
1416 enabled when polling for a minimum of 0 events (eg when
1417 iodepth_batch_complete=0).
1419 [netsplice] hostname=str
1420 [net] hostname=str The host name or IP address to use for TCP or UDP based IO.
1421 If the job is a TCP listener or UDP reader, the hostname is not
1422 used and must be omitted.
1424 [netsplice] port=int
1425 [net] port=int The TCP or UDP port to bind to or connect to.
1427 [netsplice] nodelay=bool
1428 [net] nodelay=bool Set TCP_NODELAY on TCP connections.
1430 [netsplice] protocol=str
1431 [netsplice] proto=str
1433 [net] proto=str The network protocol to use. Accepted values are:
1435 tcp Transmission control protocol
1436 udp User datagram protocol
1437 unix UNIX domain socket
1439 When the protocol is TCP or UDP, the port must also be given,
1440 as well as the hostname if the job is a TCP listener or UDP
1441 reader. For unix sockets, the normal filename option should be
1442 used and the port is invalid.
1444 [net] listen For TCP network connections, tell fio to listen for incoming
1445 connections rather than initiating an outgoing connection. The
1446 hostname must be omitted if this option is used.
1447 [net] pingpong Normal a network writer will just continue writing data, and
1448 a network reader will just consume packages. If pingpong=1
1449 is set, a writer will send its normal payload to the reader,
1450 then wait for the reader to send the same payload back. This
1451 allows fio to measure network latencies. The submission
1452 and completion latencies then measure local time spent
1453 sending or receiving, and the completion latency measures
1454 how long it took for the other end to receive and send back.
1456 [e4defrag] donorname=str
1457 File will be used as a block donor(swap extents between files)
1458 [e4defrag] inplace=int
1459 Configure donor file blocks allocation strategy
1460 0(default): Preallocate donor's file on init
1461 1 : allocate space immidietly inside defragment event,
1462 and free right after event
1466 6.0 Interpreting the output
1467 ---------------------------
1469 fio spits out a lot of output. While running, fio will display the
1470 status of the jobs created. An example of that would be:
1472 Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
1474 The characters inside the square brackets denote the current status of
1475 each thread. The possible values (in typical life cycle order) are:
1479 P Thread setup, but not started.
1481 I Thread initialized, waiting or generating necessary data.
1482 p Thread running pre-reading file(s).
1483 R Running, doing sequential reads.
1484 r Running, doing random reads.
1485 W Running, doing sequential writes.
1486 w Running, doing random writes.
1487 M Running, doing mixed sequential reads/writes.
1488 m Running, doing mixed random reads/writes.
1489 F Running, currently waiting for fsync()
1490 V Running, doing verification of written data.
1491 E Thread exited, not reaped by main thread yet.
1493 X Thread reaped, exited with an error.
1494 K Thread reaped, exited due to signal.
1496 The other values are fairly self explanatory - number of threads
1497 currently running and doing io, rate of io since last check (read speed
1498 listed first, then write speed), and the estimated completion percentage
1499 and time for the running group. It's impossible to estimate runtime of
1500 the following groups (if any). Note that the string is displayed in order,
1501 so it's possible to tell which of the jobs are currently doing what. The
1502 first character is the first job defined in the job file, and so forth.
1504 When fio is done (or interrupted by ctrl-c), it will show the data for
1505 each thread, group of threads, and disks in that order. For each data
1506 direction, the output looks like:
1508 Client1 (g=0): err= 0:
1509 write: io= 32MB, bw= 666KB/s, iops=89 , runt= 50320msec
1510 slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92
1511 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82
1512 bw (KB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
1513 cpu : usr=1.49%, sys=0.25%, ctx=7969, majf=0, minf=17
1514 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
1515 submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
1516 complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
1517 issued r/w: total=0/32768, short=0/0
1518 lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
1519 lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%
1521 The client number is printed, along with the group id and error of that
1522 thread. Below is the io statistics, here for writes. In the order listed,
1525 io= Number of megabytes io performed
1526 bw= Average bandwidth rate
1527 iops= Average IOs performed per second
1528 runt= The runtime of that thread
1529 slat= Submission latency (avg being the average, stdev being the
1530 standard deviation). This is the time it took to submit
1531 the io. For sync io, the slat is really the completion
1532 latency, since queue/complete is one operation there. This
1533 value can be in milliseconds or microseconds, fio will choose
1534 the most appropriate base and print that. In the example
1535 above, milliseconds is the best scale. Note: in --minimal mode
1536 latencies are always expressed in microseconds.
1537 clat= Completion latency. Same names as slat, this denotes the
1538 time from submission to completion of the io pieces. For
1539 sync io, clat will usually be equal (or very close) to 0,
1540 as the time from submit to complete is basically just
1541 CPU time (io has already been done, see slat explanation).
1542 bw= Bandwidth. Same names as the xlat stats, but also includes
1543 an approximate percentage of total aggregate bandwidth
1544 this thread received in this group. This last value is
1545 only really useful if the threads in this group are on the
1546 same disk, since they are then competing for disk access.
1547 cpu= CPU usage. User and system time, along with the number
1548 of context switches this thread went through, usage of
1549 system and user time, and finally the number of major
1550 and minor page faults.
1551 IO depths= The distribution of io depths over the job life time. The
1552 numbers are divided into powers of 2, so for example the
1553 16= entries includes depths up to that value but higher
1554 than the previous entry. In other words, it covers the
1555 range from 16 to 31.
1556 IO submit= How many pieces of IO were submitting in a single submit
1557 call. Each entry denotes that amount and below, until
1558 the previous entry - eg, 8=100% mean that we submitted
1559 anywhere in between 5-8 ios per submit call.
1560 IO complete= Like the above submit number, but for completions instead.
1561 IO issued= The number of read/write requests issued, and how many
1563 IO latencies= The distribution of IO completion latencies. This is the
1564 time from when IO leaves fio and when it gets completed.
1565 The numbers follow the same pattern as the IO depths,
1566 meaning that 2=1.6% means that 1.6% of the IO completed
1567 within 2 msecs, 20=12.8% means that 12.8% of the IO
1568 took more than 10 msecs, but less than (or equal to) 20 msecs.
1570 After each client has been listed, the group statistics are printed. They
1571 will look like this:
1573 Run status group 0 (all jobs):
1574 READ: io=64MB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
1575 WRITE: io=64MB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
1577 For each data direction, it prints:
1579 io= Number of megabytes io performed.
1580 aggrb= Aggregate bandwidth of threads in this group.
1581 minb= The minimum average bandwidth a thread saw.
1582 maxb= The maximum average bandwidth a thread saw.
1583 mint= The smallest runtime of the threads in that group.
1584 maxt= The longest runtime of the threads in that group.
1586 And finally, the disk statistics are printed. They will look like this:
1588 Disk stats (read/write):
1589 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
1591 Each value is printed for both reads and writes, with reads first. The
1594 ios= Number of ios performed by all groups.
1595 merge= Number of merges io the io scheduler.
1596 ticks= Number of ticks we kept the disk busy.
1597 io_queue= Total time spent in the disk queue.
1598 util= The disk utilization. A value of 100% means we kept the disk
1599 busy constantly, 50% would be a disk idling half of the time.
1601 It is also possible to get fio to dump the current output while it is
1602 running, without terminating the job. To do that, send fio the USR1 signal.
1608 For scripted usage where you typically want to generate tables or graphs
1609 of the results, fio can output the results in a semicolon separated format.
1610 The format is one long line of values, such as:
1612 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%
1613 A description of this job goes here.
1615 The job description (if provided) follows on a second line.
1617 To enable terse output, use the --minimal command line option. The first
1618 value is the version of the terse output format. If the output has to
1619 be changed for some reason, this number will be incremented by 1 to
1620 signify that change.
1622 Split up, the format is as follows:
1624 terse version, fio version, jobname, groupid, error
1626 Total IO (KB), bandwidth (KB/sec), IOPS, runtime (msec)
1627 Submission latency: min, max, mean, deviation (usec)
1628 Completion latency: min, max, mean, deviation (usec)
1629 Completion latency percentiles: 20 fields (see below)
1630 Total latency: min, max, mean, deviation (usec)
1631 Bw (KB/s): min, max, aggregate percentage of total, mean, deviation
1633 Total IO (KB), bandwidth (KB/sec), IOPS, runtime (msec)
1634 Submission latency: min, max, mean, deviation (usec)
1635 Completion latency: min, max, mean, deviation (usec)
1636 Completion latency percentiles: 20 fields (see below)
1637 Total latency: min, max, mean, deviation (usec)
1638 Bw (KB/s): min, max, aggregate percentage of total, mean, deviation
1639 CPU usage: user, system, context switches, major faults, minor faults
1640 IO depths: <=1, 2, 4, 8, 16, 32, >=64
1641 IO latencies microseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000
1642 IO latencies milliseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, 2000, >=2000
1643 Disk utilization: Disk name, Read ios, write ios,
1644 Read merges, write merges,
1645 Read ticks, write ticks,
1646 Time spent in queue, disk utilization percentage
1647 Additional Info (dependant on continue_on_error, default off): total # errors, first error code
1649 Additional Info (dependant on description being set): Text description
1651 Completion latency percentiles can be a grouping of up to 20 sets, so
1652 for the terse output fio writes all of them. Each field will look like this:
1656 which is the Xth percentile, and the usec latency associated with it.
1658 For disk utilization, all disks used by fio are shown. So for each disk
1659 there will be a disk utilization section.
1662 8.0 Trace file format
1663 ---------------------
1664 There are two trace file format that you can encounter. The older (v1) format
1665 is unsupported since version 1.20-rc3 (March 2008). It will still be described
1666 below in case that you get an old trace and want to understand it.
1668 In any case the trace is a simple text file with a single action per line.
1671 8.1 Trace file format v1
1672 ------------------------
1673 Each line represents a single io action in the following format:
1677 where rw=0/1 for read/write, and the offset and length entries being in bytes.
1679 This format is not supported in Fio versions => 1.20-rc3.
1682 8.2 Trace file format v2
1683 ------------------------
1684 The second version of the trace file format was added in Fio version 1.17.
1685 It allows to access more then one file per trace and has a bigger set of
1686 possible file actions.
1688 The first line of the trace file has to be:
1692 Following this can be lines in two different formats, which are described below.
1694 The file management format:
1698 The filename is given as an absolute path. The action can be one of these:
1700 add Add the given filename to the trace
1701 open Open the file with the given filename. The filename has to have
1702 been added with the add action before.
1703 close Close the file with the given filename. The file has to have been
1707 The file io action format:
1709 filename action offset length
1711 The filename is given as an absolute path, and has to have been added and opened
1712 before it can be used with this format. The offset and length are given in
1713 bytes. The action can be one of these:
1715 wait Wait for 'offset' microseconds. Everything below 100 is discarded.
1716 read Read 'length' bytes beginning from 'offset'
1717 write Write 'length' bytes beginning from 'offset'
1718 sync fsync() the file
1719 datasync fdatasync() the file
1720 trim trim the given file from the given 'offset' for 'length' bytes
1723 9.0 CPU idleness profiling
1725 In some cases, we want to understand CPU overhead in a test. For example,
1726 we test patches for the specific goodness of whether they reduce CPU usage.
1727 fio implements a balloon approach to create a thread per CPU that runs at
1728 idle priority, meaning that it only runs when nobody else needs the cpu.
1729 By measuring the amount of work completed by the thread, idleness of each
1730 CPU can be derived accordingly.
1732 An unit work is defined as touching a full page of unsigned characters. Mean
1733 and standard deviation of time to complete an unit work is reported in "unit
1734 work" section. Options can be chosen to report detailed percpu idleness or
1735 overall system idleness by aggregating percpu stats.
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