8 5. Detailed list of parameters
13 1.0 Overview and history
14 ------------------------
15 fio was originally written to save me the hassle of writing special test
16 case programs when I wanted to test a specific workload, either for
17 performance reasons or to find/reproduce a bug. The process of writing
18 such a test app can be tiresome, especially if you have to do it often.
19 Hence I needed a tool that would be able to simulate a given io workload
20 without resorting to writing a tailored test case again and again.
22 A test work load is difficult to define, though. There can be any number
23 of processes or threads involved, and they can each be using their own
24 way of generating io. You could have someone dirtying large amounts of
25 memory in an memory mapped file, or maybe several threads issuing
26 reads using asynchronous io. fio needed to be flexible enough to
27 simulate both of these cases, and many more.
31 The first step in getting fio to simulate a desired io workload, is
32 writing a job file describing that specific setup. A job file may contain
33 any number of threads and/or files - the typical contents of the job file
34 is a global section defining shared parameters, and one or more job
35 sections describing the jobs involved. When run, fio parses this file
36 and sets everything up as described. If we break down a job from top to
37 bottom, it contains the following basic parameters:
39 IO type Defines the io pattern issued to the file(s).
40 We may only be reading sequentially from this
41 file(s), or we may be writing randomly. Or even
42 mixing reads and writes, sequentially or randomly.
44 Block size In how large chunks are we issuing io? This may be
45 a single value, or it may describe a range of
48 IO size How much data are we going to be reading/writing.
50 IO engine How do we issue io? We could be memory mapping the
51 file, we could be using regular read/write, we
52 could be using splice, async io, syslet, or even
55 IO depth If the io engine is async, how large a queuing
56 depth do we want to maintain?
58 IO type Should we be doing buffered io, or direct/raw io?
60 Num files How many files are we spreading the workload over.
62 Num threads How many threads or processes should we spread
65 The above are the basic parameters defined for a workload, in addition
66 there's a multitude of parameters that modify other aspects of how this
72 See the README file for command line parameters, there are only a few
75 Running fio is normally the easiest part - you just give it the job file
76 (or job files) as parameters:
80 and it will start doing what the job_file tells it to do. You can give
81 more than one job file on the command line, fio will serialize the running
82 of those files. Internally that is the same as using the 'stonewall'
83 parameter described the the parameter section.
85 If the job file contains only one job, you may as well just give the
86 parameters on the command line. The command line parameters are identical
87 to the job parameters, with a few extra that control global parameters
88 (see README). For example, for the job file parameter iodepth=2, the
89 mirror command line option would be --iodepth 2 or --iodepth=2. You can
90 also use the command line for giving more than one job entry. For each
91 --name option that fio sees, it will start a new job with that name.
92 Command line entries following a --name entry will apply to that job,
93 until there are no more entries or a new --name entry is seen. This is
94 similar to the job file options, where each option applies to the current
95 job until a new [] job entry is seen.
97 fio does not need to run as root, except if the files or devices specified
98 in the job section requires that. Some other options may also be restricted,
99 such as memory locking, io scheduler switching, and decreasing the nice value.
104 As previously described, fio accepts one or more job files describing
105 what it is supposed to do. The job file format is the classic ini file,
106 where the names enclosed in [] brackets define the job name. You are free
107 to use any ascii name you want, except 'global' which has special meaning.
108 A global section sets defaults for the jobs described in that file. A job
109 may override a global section parameter, and a job file may even have
110 several global sections if so desired. A job is only affected by a global
111 section residing above it. If the first character in a line is a ';' or a
112 '#', the entire line is discarded as a comment.
114 So let's look at a really simple job file that defines two processes, each
115 randomly reading from a 128MiB file.
117 ; -- start job file --
128 As you can see, the job file sections themselves are empty as all the
129 described parameters are shared. As no filename= option is given, fio
130 makes up a filename for each of the jobs as it sees fit. On the command
131 line, this job would look as follows:
133 $ fio --name=global --rw=randread --size=128m --name=job1 --name=job2
136 Let's look at an example that has a number of processes writing randomly
139 ; -- start job file --
151 Here we have no global section, as we only have one job defined anyway.
152 We want to use async io here, with a depth of 4 for each file. We also
153 increased the buffer size used to 32KiB and define numjobs to 4 to
154 fork 4 identical jobs. The result is 4 processes each randomly writing
155 to their own 64MiB file. Instead of using the above job file, you could
156 have given the parameters on the command line. For this case, you would
159 $ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4
161 fio also supports environment variable expansion in job files. Any
162 substring of the form "${VARNAME}" as part of an option value (in other
163 words, on the right of the `='), will be expanded to the value of the
164 environment variable called VARNAME. If no such environment variable
165 is defined, or VARNAME is the empty string, the empty string will be
168 As an example, let's look at a sample fio invocation and job file:
170 $ SIZE=64m NUMJOBS=4 fio jobfile.fio
172 ; -- start job file --
179 This will expand to the following equivalent job file at runtime:
181 ; -- start job file --
188 fio ships with a few example job files, you can also look there for
192 5.0 Detailed list of parameters
193 -------------------------------
195 This section describes in details each parameter associated with a job.
196 Some parameters take an option of a given type, such as an integer or
197 a string. The following types are used:
199 str String. This is a sequence of alpha characters.
200 int Integer. A whole number value, can be negative. If prefixed with
201 0x, the integer is assumed to be of base 16 (hexadecimal).
202 time Integer with possible time postfix. In seconds unless otherwise
203 specified, use eg 10m for 10 minutes. Accepts s/m/h for seconds,
205 siint SI integer. A whole number value, which may contain a postfix
206 describing the base of the number. Accepted postfixes are k/m/g,
207 meaning kilo, mega, and giga. So if you want to specify 4096,
208 you could either write out '4096' or just give 4k. The postfixes
209 signify base 2 values, so 1024 is 1k and 1024k is 1m and so on.
210 If the option accepts an upper and lower range, use a colon ':'
211 or minus '-' to separate such values. See irange.
212 bool Boolean. Usually parsed as an integer, however only defined for
213 true and false (1 and 0).
214 irange Integer range with postfix. Allows value range to be given, such
215 as 1024-4096. A colon may also be used as the separator, eg
216 1k:4k. If the option allows two sets of ranges, they can be
217 specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see
220 With the above in mind, here follows the complete list of fio job
223 name=str ASCII name of the job. This may be used to override the
224 name printed by fio for this job. Otherwise the job
225 name is used. On the command line this parameter has the
226 special purpose of also signaling the start of a new
229 description=str Text description of the job. Doesn't do anything except
230 dump this text description when this job is run. It's
233 directory=str Prefix filenames with this directory. Used to places files
234 in a different location than "./".
236 filename=str Fio normally makes up a filename based on the job name,
237 thread number, and file number. If you want to share
238 files between threads in a job or several jobs, specify
239 a filename for each of them to override the default. If
240 the ioengine used is 'net', the filename is the host, port,
241 and protocol to use in the format of =host/port/protocol.
242 See ioengine=net for more. If the ioengine is file based, you
243 can specify a number of files by separating the names with a
244 ':' colon. So if you wanted a job to open /dev/sda and /dev/sdb
245 as the two working files, you would use
246 filename=/dev/sda:/dev/sdb. '-' is a reserved name, meaning
247 stdin or stdout. Which of the two depends on the read/write
250 opendir=str Tell fio to recursively add any file it can find in this
251 directory and down the file system tree.
253 lockfile=str Fio defaults to not doing any locking files before it does
254 IO to them. If a file or file descriptor is shared, fio
255 can serialize IO to that file to make the end result
256 consistent. This is usual for emulating real workloads that
257 share files. The lock modes are:
259 none No locking. The default.
260 exclusive Only one thread/process may do IO,
261 excluding all others.
262 readwrite Read-write locking on the file. Many
263 readers may access the file at the
264 same time, but writes get exclusive
267 The option may be post-fixed with a lock batch number. If
268 set, then each thread/process may do that amount of IOs to
269 the file before giving up the lock. Since lock acquisition is
270 expensive, batching the lock/unlocks will speed up IO.
273 rw=str Type of io pattern. Accepted values are:
275 read Sequential reads
276 write Sequential writes
277 randwrite Random writes
278 randread Random reads
279 rw Sequential mixed reads and writes
280 randrw Random mixed reads and writes
282 For the mixed io types, the default is to split them 50/50.
283 For certain types of io the result may still be skewed a bit,
284 since the speed may be different. It is possible to specify
285 a number of IO's to do before getting a new offset - this
286 is only useful for random IO, where fio would normally
287 generate a new random offset for every IO. If you append
288 eg 8 to randread, you would get a new random offset for
289 every 8 IO's. The result would be a seek for only every 8
290 IO's, instead of for every IO. Use rw=randread:8 to specify
293 randrepeat=bool For random IO workloads, seed the generator in a predictable
294 way so that results are repeatable across repetitions.
296 fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
297 on what IO patterns it is likely to issue. Sometimes you
298 want to test specific IO patterns without telling the
299 kernel about it, in which case you can disable this option.
300 If set, fio will use POSIX_FADV_SEQUENTIAL for sequential
301 IO and POSIX_FADV_RANDOM for random IO.
303 size=siint The total size of file io for this job. Fio will run until
304 this many bytes has been transferred, unless runtime is
305 limited by other options (such as 'runtime', for instance).
306 Unless specific nr_files and filesize options are given,
307 fio will divide this size between the available files
308 specified by the job.
310 filesize=siint Individual file sizes. May be a range, in which case fio
311 will select sizes for files at random within the given range
312 and limited to 'size' in total (if that is given). If not
313 given, each created file is the same size.
315 fill_device=bool Sets size to something really large and waits for ENOSPC (no
316 space left on device) as the terminating condition. Only makes
317 sense with sequential write.
320 bs=siint The block size used for the io units. Defaults to 4k. Values
321 can be given for both read and writes. If a single siint is
322 given, it will apply to both. If a second siint is specified
323 after a comma, it will apply to writes only. In other words,
324 the format is either bs=read_and_write or bs=read,write.
325 bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
326 for writes. If you only wish to set the write size, you
327 can do so by passing an empty read size - bs=,8k will set
328 8k for writes and leave the read default value.
330 blocksize_range=irange
331 bsrange=irange Instead of giving a single block size, specify a range
332 and fio will mix the issued io block sizes. The issued
333 io unit will always be a multiple of the minimum value
334 given (also see bs_unaligned). Applies to both reads and
335 writes, however a second range can be given after a comma.
338 bssplit=str Sometimes you want even finer grained control of the
339 block sizes issued, not just an even split between them.
340 This option allows you to weight various block sizes,
341 so that you are able to define a specific amount of
342 block sizes issued. The format for this option is:
344 bssplit=blocksize/percentage:blocksize/percentage
346 for as many block sizes as needed. So if you want to define
347 a workload that has 50% 64k blocks, 10% 4k blocks, and
348 40% 32k blocks, you would write:
350 bssplit=4k/10:64k/50:32k/40
352 Ordering does not matter. If the percentage is left blank,
353 fio will fill in the remaining values evenly. So a bssplit
354 option like this one:
356 bssplit=4k/50:1k/:32k/
358 would have 50% 4k ios, and 25% 1k and 32k ios. The percentages
359 always add up to 100, if bssplit is given a range that adds
360 up to more, it will error out.
363 bs_unaligned If this option is given, any byte size value within bsrange
364 may be used as a block range. This typically wont work with
365 direct IO, as that normally requires sector alignment.
367 zero_buffers If this option is given, fio will init the IO buffers to
368 all zeroes. The default is to fill them with random data.
370 refill_buffers If this option is given, fio will refill the IO buffers
371 on every submit. The default is to only fill it at init
372 time and reuse that data. Only makes sense if zero_buffers
373 isn't specified, naturally. If data verification is enabled,
374 refill_buffers is also automatically enabled.
376 nrfiles=int Number of files to use for this job. Defaults to 1.
378 openfiles=int Number of files to keep open at the same time. Defaults to
379 the same as nrfiles, can be set smaller to limit the number
382 file_service_type=str Defines how fio decides which file from a job to
383 service next. The following types are defined:
385 random Just choose a file at random.
387 roundrobin Round robin over open files. This
390 sequential Finish one file before moving on to
391 the next. Multiple files can still be
392 open depending on 'openfiles'.
394 The string can have a number appended, indicating how
395 often to switch to a new file. So if option random:4 is
396 given, fio will switch to a new random file after 4 ios
399 ioengine=str Defines how the job issues io to the file. The following
402 sync Basic read(2) or write(2) io. lseek(2) is
403 used to position the io location.
405 psync Basic pread(2) or pwrite(2) io.
407 vsync Basic readv(2) or writev(2) IO.
409 libaio Linux native asynchronous io. Note that Linux
410 may only support queued behaviour with
411 non-buffered IO (set direct=1 or buffered=0).
413 posixaio glibc posix asynchronous io.
415 solarisaio Solaris native asynchronous io.
417 mmap File is memory mapped and data copied
418 to/from using memcpy(3).
420 splice splice(2) is used to transfer the data and
421 vmsplice(2) to transfer data from user
424 syslet-rw Use the syslet system calls to make
425 regular read/write async.
427 sg SCSI generic sg v3 io. May either be
428 synchronous using the SG_IO ioctl, or if
429 the target is an sg character device
430 we use read(2) and write(2) for asynchronous
433 null Doesn't transfer any data, just pretends
434 to. This is mainly used to exercise fio
435 itself and for debugging/testing purposes.
437 net Transfer over the network to given host:port.
438 'filename' must be set appropriately to
439 filename=host/port/protocol regardless of send
440 or receive, if the latter only the port
441 argument is used. 'host' may be an IP address
442 or hostname, port is the port number to be used,
443 and protocol may be 'udp' or 'tcp'. If no
444 protocol is given, TCP is used.
446 netsplice Like net, but uses splice/vmsplice to
447 map data and send/receive.
449 cpuio Doesn't transfer any data, but burns CPU
450 cycles according to the cpuload= and
451 cpucycle= options. Setting cpuload=85
452 will cause that job to do nothing but burn
453 85% of the CPU. In case of SMP machines,
454 use numjobs=<no_of_cpu> to get desired CPU
455 usage, as the cpuload only loads a single
456 CPU at the desired rate.
458 guasi The GUASI IO engine is the Generic Userspace
459 Asyncronous Syscall Interface approach
462 http://www.xmailserver.org/guasi-lib.html
464 for more info on GUASI.
466 external Prefix to specify loading an external
467 IO engine object file. Append the engine
468 filename, eg ioengine=external:/tmp/foo.o
469 to load ioengine foo.o in /tmp.
471 iodepth=int This defines how many io units to keep in flight against
472 the file. The default is 1 for each file defined in this
473 job, can be overridden with a larger value for higher
476 iodepth_batch_submit=int
477 iodepth_batch=int This defines how many pieces of IO to submit at once.
478 It defaults to 1 which means that we submit each IO
479 as soon as it is available, but can be raised to submit
480 bigger batches of IO at the time.
482 iodepth_batch_complete=int This defines how many pieces of IO to retrieve
483 at once. It defaults to 1 which means that we'll ask
484 for a minimum of 1 IO in the retrieval process from
485 the kernel. The IO retrieval will go on until we
486 hit the limit set by iodepth_low. If this variable is
487 set to 0, then fio will always check for completed
488 events before queuing more IO. This helps reduce
489 IO latency, at the cost of more retrieval system calls.
491 iodepth_low=int The low water mark indicating when to start filling
492 the queue again. Defaults to the same as iodepth, meaning
493 that fio will attempt to keep the queue full at all times.
494 If iodepth is set to eg 16 and iodepth_low is set to 4, then
495 after fio has filled the queue of 16 requests, it will let
496 the depth drain down to 4 before starting to fill it again.
498 direct=bool If value is true, use non-buffered io. This is usually
501 buffered=bool If value is true, use buffered io. This is the opposite
502 of the 'direct' option. Defaults to true.
504 offset=siint Start io at the given offset in the file. The data before
505 the given offset will not be touched. This effectively
506 caps the file size at real_size - offset.
508 fsync=int If writing to a file, issue a sync of the dirty data
509 for every number of blocks given. For example, if you give
510 32 as a parameter, fio will sync the file for every 32
511 writes issued. If fio is using non-buffered io, we may
512 not sync the file. The exception is the sg io engine, which
513 synchronizes the disk cache anyway.
515 overwrite=bool If true, writes to a file will always overwrite existing
516 data. If the file doesn't already exist, it will be
517 created before the write phase begins. If the file exists
518 and is large enough for the specified write phase, nothing
521 end_fsync=bool If true, fsync file contents when the job exits.
523 fsync_on_close=bool If true, fio will fsync() a dirty file on close.
524 This differs from end_fsync in that it will happen on every
525 file close, not just at the end of the job.
527 rwmixread=int How large a percentage of the mix should be reads.
529 rwmixwrite=int How large a percentage of the mix should be writes. If both
530 rwmixread and rwmixwrite is given and the values do not add
531 up to 100%, the latter of the two will be used to override
534 norandommap Normally fio will cover every block of the file when doing
535 random IO. If this option is given, fio will just get a
536 new random offset without looking at past io history. This
537 means that some blocks may not be read or written, and that
538 some blocks may be read/written more than once. This option
539 is mutually exclusive with verify= if and only if multiple
540 blocksizes (via bsrange=) are used, since fio only tracks
541 complete rewrites of blocks.
543 softrandommap See norandommap. If fio runs with the random block map enabled
544 and it fails to allocate the map, if this option is set it
545 will continue without a random block map. As coverage will
546 not be as complete as with random maps, this option is
549 nice=int Run the job with the given nice value. See man nice(2).
551 prio=int Set the io priority value of this job. Linux limits us to
552 a positive value between 0 and 7, with 0 being the highest.
555 prioclass=int Set the io priority class. See man ionice(1).
557 thinktime=int Stall the job x microseconds after an io has completed before
558 issuing the next. May be used to simulate processing being
559 done by an application. See thinktime_blocks and
563 Only valid if thinktime is set - pretend to spend CPU time
564 doing something with the data received, before falling back
565 to sleeping for the rest of the period specified by
569 Only valid if thinktime is set - control how many blocks
570 to issue, before waiting 'thinktime' usecs. If not set,
571 defaults to 1 which will make fio wait 'thinktime' usecs
574 rate=int Cap the bandwidth used by this job to this number of KiB/sec.
576 ratemin=int Tell fio to do whatever it can to maintain at least this
577 bandwidth. Failing to meet this requirement, will cause
580 rate_iops=int Cap the bandwidth to this number of IOPS. Basically the same
581 as rate, just specified independently of bandwidth. If the
582 job is given a block size range instead of a fixed value,
583 the smallest block size is used as the metric.
585 rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
588 ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
591 cpumask=int Set the CPU affinity of this job. The parameter given is a
592 bitmask of allowed CPU's the job may run on. So if you want
593 the allowed CPUs to be 1 and 5, you would pass the decimal
594 value of (1 << 1 | 1 << 5), or 34. See man
595 sched_setaffinity(2). This may not work on all supported
596 operating systems or kernel versions. This option doesn't
597 work well for a higher CPU count than what you can store in
598 an integer mask, so it can only control cpus 1-32. For
599 boxes with larger CPU counts, use cpus_allowed.
601 cpus_allowed=str Controls the same options as cpumask, but it allows a text
602 setting of the permitted CPUs instead. So to use CPUs 1 and
603 5, you would specify cpus_allowed=1,5. This options also
604 allows a range of CPUs. Say you wanted a binding to CPUs
605 1, 5, and 8-15, you would set cpus_allowed=1,5,8-15.
607 startdelay=time Start this job the specified number of seconds after fio
608 has started. Only useful if the job file contains several
609 jobs, and you want to delay starting some jobs to a certain
612 runtime=time Tell fio to terminate processing after the specified number
613 of seconds. It can be quite hard to determine for how long
614 a specified job will run, so this parameter is handy to
615 cap the total runtime to a given time.
617 time_based If set, fio will run for the duration of the runtime
618 specified even if the file(s) are completely read or
619 written. It will simply loop over the same workload
620 as many times as the runtime allows.
622 ramp_time=time If set, fio will run the specified workload for this amount
623 of time before logging any performance numbers. Useful for
624 letting performance settle before logging results, thus
625 minimizing the runtime required for stable results. Note
626 that the ramp_time is considered lead in time for a job,
627 thus it will increase the total runtime if a special timeout
628 or runtime is specified.
630 invalidate=bool Invalidate the buffer/page cache parts for this file prior
631 to starting io. Defaults to true.
633 sync=bool Use sync io for buffered writes. For the majority of the
634 io engines, this means using O_SYNC.
637 mem=str Fio can use various types of memory as the io unit buffer.
638 The allowed values are:
640 malloc Use memory from malloc(3) as the buffers.
642 shm Use shared memory as the buffers. Allocated
645 shmhuge Same as shm, but use huge pages as backing.
647 mmap Use mmap to allocate buffers. May either be
648 anonymous memory, or can be file backed if
649 a filename is given after the option. The
650 format is mem=mmap:/path/to/file.
652 mmaphuge Use a memory mapped huge file as the buffer
653 backing. Append filename after mmaphuge, ala
654 mem=mmaphuge:/hugetlbfs/file
656 The area allocated is a function of the maximum allowed
657 bs size for the job, multiplied by the io depth given. Note
658 that for shmhuge and mmaphuge to work, the system must have
659 free huge pages allocated. This can normally be checked
660 and set by reading/writing /proc/sys/vm/nr_hugepages on a
661 Linux system. Fio assumes a huge page is 4MiB in size. So
662 to calculate the number of huge pages you need for a given
663 job file, add up the io depth of all jobs (normally one unless
664 iodepth= is used) and multiply by the maximum bs set. Then
665 divide that number by the huge page size. You can see the
666 size of the huge pages in /proc/meminfo. If no huge pages
667 are allocated by having a non-zero number in nr_hugepages,
668 using mmaphuge or shmhuge will fail. Also see hugepage-size.
670 mmaphuge also needs to have hugetlbfs mounted and the file
671 location should point there. So if it's mounted in /huge,
672 you would use mem=mmaphuge:/huge/somefile.
675 Defines the size of a huge page. Must at least be equal
676 to the system setting, see /proc/meminfo. Defaults to 4MiB.
677 Should probably always be a multiple of megabytes, so using
678 hugepage-size=Xm is the preferred way to set this to avoid
679 setting a non-pow-2 bad value.
681 exitall When one job finishes, terminate the rest. The default is
682 to wait for each job to finish, sometimes that is not the
685 bwavgtime=int Average the calculated bandwidth over the given time. Value
686 is specified in milliseconds.
688 create_serialize=bool If true, serialize the file creating for the jobs.
689 This may be handy to avoid interleaving of data
690 files, which may greatly depend on the filesystem
691 used and even the number of processors in the system.
693 create_fsync=bool fsync the data file after creation. This is the
696 create_on_open=bool Don't pre-setup the files for IO, just create open()
697 when it's time to do IO to that file.
699 unlink=bool Unlink the job files when done. Not the default, as repeated
700 runs of that job would then waste time recreating the file
703 loops=int Run the specified number of iterations of this job. Used
704 to repeat the same workload a given number of times. Defaults
707 do_verify=bool Run the verify phase after a write phase. Only makes sense if
708 verify is set. Defaults to 1.
710 verify=str If writing to a file, fio can verify the file contents
711 after each iteration of the job. The allowed values are:
713 md5 Use an md5 sum of the data area and store
714 it in the header of each block.
716 crc64 Use an experimental crc64 sum of the data
717 area and store it in the header of each
720 crc32c Use a crc32c sum of the data area and store
721 it in the header of each block.
723 crc32c-intel Use hardware assisted crc32c calcuation
724 provided on SSE4.2 enabled processors.
726 crc32 Use a crc32 sum of the data area and store
727 it in the header of each block.
729 crc16 Use a crc16 sum of the data area and store
730 it in the header of each block.
732 crc7 Use a crc7 sum of the data area and store
733 it in the header of each block.
735 sha512 Use sha512 as the checksum function.
737 sha256 Use sha256 as the checksum function.
739 meta Write extra information about each io
740 (timestamp, block number etc.). The block
743 null Only pretend to verify. Useful for testing
744 internals with ioengine=null, not for much
747 This option can be used for repeated burn-in tests of a
748 system to make sure that the written data is also
751 verifysort=bool If set, fio will sort written verify blocks when it deems
752 it faster to read them back in a sorted manner. This is
753 often the case when overwriting an existing file, since
754 the blocks are already laid out in the file system. You
755 can ignore this option unless doing huge amounts of really
756 fast IO where the red-black tree sorting CPU time becomes
759 verify_offset=siint Swap the verification header with data somewhere else
760 in the block before writing. Its swapped back before
763 verify_interval=siint Write the verification header at a finer granularity
764 than the blocksize. It will be written for chunks the
765 size of header_interval. blocksize should divide this
768 verify_pattern=int If set, fio will fill the io buffers with this
769 pattern. Fio defaults to filling with totally random
770 bytes, but sometimes it's interesting to fill with a known
771 pattern for io verification purposes. Depending on the
772 width of the pattern, fio will fill 1/2/3/4 bytes of the
773 buffer at the time. The verify_pattern cannot be larger than
776 verify_fatal=bool Normally fio will keep checking the entire contents
777 before quitting on a block verification failure. If this
778 option is set, fio will exit the job on the first observed
781 stonewall Wait for preceeding jobs in the job file to exit, before
782 starting this one. Can be used to insert serialization
783 points in the job file. A stone wall also implies starting
784 a new reporting group.
786 new_group Start a new reporting group. If this option isn't given,
787 jobs in a file will be part of the same reporting group
788 unless separated by a stone wall (or if it's a group
789 by itself, with the numjobs option).
791 numjobs=int Create the specified number of clones of this job. May be
792 used to setup a larger number of threads/processes doing
793 the same thing. We regard that grouping of jobs as a
796 group_reporting If 'numjobs' is set, it may be interesting to display
797 statistics for the group as a whole instead of for each
798 individual job. This is especially true of 'numjobs' is
799 large, looking at individual thread/process output quickly
800 becomes unwieldy. If 'group_reporting' is specified, fio
801 will show the final report per-group instead of per-job.
803 thread fio defaults to forking jobs, however if this option is
804 given, fio will use pthread_create(3) to create threads
807 zonesize=siint Divide a file into zones of the specified size. See zoneskip.
809 zoneskip=siint Skip the specified number of bytes when zonesize data has
810 been read. The two zone options can be used to only do
811 io on zones of a file.
813 write_iolog=str Write the issued io patterns to the specified file. See
816 read_iolog=str Open an iolog with the specified file name and replay the
817 io patterns it contains. This can be used to store a
818 workload and replay it sometime later. The iolog given
819 may also be a blktrace binary file, which allows fio
820 to replay a workload captured by blktrace. See blktrace
821 for how to capture such logging data. For blktrace replay,
822 the file needs to be turned into a blkparse binary data
823 file first (blktrace <device> -d file_for_fio.bin).
825 write_bw_log=str If given, write a bandwidth log of the jobs in this job
826 file. Can be used to store data of the bandwidth of the
827 jobs in their lifetime. The included fio_generate_plots
828 script uses gnuplot to turn these text files into nice
829 graphs. See write_log_log for behaviour of given
830 filename. For this option, the postfix is _bw.log.
832 write_lat_log=str Same as write_bw_log, except that this option stores io
833 completion latencies instead. If no filename is given
834 with this option, the default filename of "jobname_type.log"
835 is used. Even if the filename is given, fio will still
836 append the type of log. So if one specifies
840 The actual log names will be foo_clat.log and foo_slat.log.
841 This helps fio_generate_plot fine the logs automatically.
843 lockmem=siint Pin down the specified amount of memory with mlock(2). Can
844 potentially be used instead of removing memory or booting
845 with less memory to simulate a smaller amount of memory.
847 exec_prerun=str Before running this job, issue the command specified
850 exec_postrun=str After the job completes, issue the command specified
853 ioscheduler=str Attempt to switch the device hosting the file to the specified
854 io scheduler before running.
856 cpuload=int If the job is a CPU cycle eater, attempt to use the specified
857 percentage of CPU cycles.
859 cpuchunks=int If the job is a CPU cycle eater, split the load into
860 cycles of the given time. In milliseconds.
862 disk_util=bool Generate disk utilization statistics, if the platform
863 supports it. Defaults to on.
865 disable_clat=bool Disable measurements of completion latency numbers. Useful
866 only for cutting back the number of calls to gettimeofday,
867 as that does impact performance at really high IOPS rates.
868 Note that to really get rid of a large amount of these
869 calls, this option must be used with disable_slat and
872 disable_slat=bool Disable measurements of submission latency numbers. See
875 disable_bw=bool Disable measurements of throughput/bandwidth numbers. See
878 gtod_reduce=bool Enable all of the gettimeofday() reducing options
879 (disable_clat, disable_slat, disable_bw) plus reduce
880 precision of the timeout somewhat to really shrink
881 the gettimeofday() call count. With this option enabled,
882 we only do about 0.4% of the gtod() calls we would have
883 done if all time keeping was enabled.
885 gtod_cpu=int Sometimes it's cheaper to dedicate a single thread of
886 execution to just getting the current time. Fio (and
887 databases, for instance) are very intensive on gettimeofday()
888 calls. With this option, you can set one CPU aside for
889 doing nothing but logging current time to a shared memory
890 location. Then the other threads/processes that run IO
891 workloads need only copy that segment, instead of entering
892 the kernel with a gettimeofday() call. The CPU set aside
893 for doing these time calls will be excluded from other
894 uses. Fio will manually clear it from the CPU mask of other
898 6.0 Interpreting the output
899 ---------------------------
901 fio spits out a lot of output. While running, fio will display the
902 status of the jobs created. An example of that would be:
904 Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
906 The characters inside the square brackets denote the current status of
907 each thread. The possible values (in typical life cycle order) are:
911 P Thread setup, but not started.
913 I Thread initialized, waiting.
914 R Running, doing sequential reads.
915 r Running, doing random reads.
916 W Running, doing sequential writes.
917 w Running, doing random writes.
918 M Running, doing mixed sequential reads/writes.
919 m Running, doing mixed random reads/writes.
920 F Running, currently waiting for fsync()
921 V Running, doing verification of written data.
922 E Thread exited, not reaped by main thread yet.
925 The other values are fairly self explanatory - number of threads
926 currently running and doing io, rate of io since last check (read speed
927 listed first, then write speed), and the estimated completion percentage
928 and time for the running group. It's impossible to estimate runtime of
929 the following groups (if any).
931 When fio is done (or interrupted by ctrl-c), it will show the data for
932 each thread, group of threads, and disks in that order. For each data
933 direction, the output looks like:
935 Client1 (g=0): err= 0:
936 write: io= 32MiB, bw= 666KiB/s, runt= 50320msec
937 slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92
938 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82
939 bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
940 cpu : usr=1.49%, sys=0.25%, ctx=7969, majf=0, minf=17
941 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
942 submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
943 complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
944 issued r/w: total=0/32768, short=0/0
945 lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
946 lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%
948 The client number is printed, along with the group id and error of that
949 thread. Below is the io statistics, here for writes. In the order listed,
952 io= Number of megabytes io performed
953 bw= Average bandwidth rate
954 runt= The runtime of that thread
955 slat= Submission latency (avg being the average, stdev being the
956 standard deviation). This is the time it took to submit
957 the io. For sync io, the slat is really the completion
958 latency, since queue/complete is one operation there. This
959 value can be in milliseconds or microseconds, fio will choose
960 the most appropriate base and print that. In the example
961 above, milliseconds is the best scale.
962 clat= Completion latency. Same names as slat, this denotes the
963 time from submission to completion of the io pieces. For
964 sync io, clat will usually be equal (or very close) to 0,
965 as the time from submit to complete is basically just
966 CPU time (io has already been done, see slat explanation).
967 bw= Bandwidth. Same names as the xlat stats, but also includes
968 an approximate percentage of total aggregate bandwidth
969 this thread received in this group. This last value is
970 only really useful if the threads in this group are on the
971 same disk, since they are then competing for disk access.
972 cpu= CPU usage. User and system time, along with the number
973 of context switches this thread went through, usage of
974 system and user time, and finally the number of major
975 and minor page faults.
976 IO depths= The distribution of io depths over the job life time. The
977 numbers are divided into powers of 2, so for example the
978 16= entries includes depths up to that value but higher
979 than the previous entry. In other words, it covers the
981 IO submit= How many pieces of IO were submitting in a single submit
982 call. Each entry denotes that amount and below, until
983 the previous entry - eg, 8=100% mean that we submitted
984 anywhere in between 5-8 ios per submit call.
985 IO complete= Like the above submit number, but for completions instead.
986 IO issued= The number of read/write requests issued, and how many
988 IO latencies= The distribution of IO completion latencies. This is the
989 time from when IO leaves fio and when it gets completed.
990 The numbers follow the same pattern as the IO depths,
991 meaning that 2=1.6% means that 1.6% of the IO completed
992 within 2 msecs, 20=12.8% means that 12.8% of the IO
993 took more than 10 msecs, but less than (or equal to) 20 msecs.
995 After each client has been listed, the group statistics are printed. They
998 Run status group 0 (all jobs):
999 READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
1000 WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
1002 For each data direction, it prints:
1004 io= Number of megabytes io performed.
1005 aggrb= Aggregate bandwidth of threads in this group.
1006 minb= The minimum average bandwidth a thread saw.
1007 maxb= The maximum average bandwidth a thread saw.
1008 mint= The smallest runtime of the threads in that group.
1009 maxt= The longest runtime of the threads in that group.
1011 And finally, the disk statistics are printed. They will look like this:
1013 Disk stats (read/write):
1014 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
1016 Each value is printed for both reads and writes, with reads first. The
1019 ios= Number of ios performed by all groups.
1020 merge= Number of merges io the io scheduler.
1021 ticks= Number of ticks we kept the disk busy.
1022 io_queue= Total time spent in the disk queue.
1023 util= The disk utilization. A value of 100% means we kept the disk
1024 busy constantly, 50% would be a disk idling half of the time.
1030 For scripted usage where you typically want to generate tables or graphs
1031 of the results, fio can output the results in a semicolon separated format.
1032 The format is one long line of values, such as:
1034 client1;0;0;1906777;1090804;1790;0;0;0.000000;0.000000;0;0;0.000000;0.000000;929380;1152890;25.510151%;1078276.333333;128948.113404;0;0;0;0;0;0.000000;0.000000;0;0;0.000000;0.000000;0;0;0.000000%;0.000000;0.000000;100.000000%;0.000000%;324;100.0%;0.0%;0.0%;0.0%;0.0%;0.0%;0.0%;100.0%;0.0%;0.0%;0.0%;0.0%;0.0%
1035 ;0.0%;0.0%;0.0%;0.0%;0.0%
1037 To enable terse output, use the --minimal command line option.
1039 Split up, the format is as follows:
1041 jobname, groupid, error
1043 KiB IO, bandwidth (KiB/sec), runtime (msec)
1044 Submission latency: min, max, mean, deviation
1045 Completion latency: min, max, mean, deviation
1046 Bw: min, max, aggregate percentage of total, mean, deviation
1048 KiB IO, bandwidth (KiB/sec), runtime (msec)
1049 Submission latency: min, max, mean, deviation
1050 Completion latency: min, max, mean, deviation
1051 Bw: min, max, aggregate percentage of total, mean, deviation
1052 CPU usage: user, system, context switches, major faults, minor faults
1053 IO depths: <=1, 2, 4, 8, 16, 32, >=64
1054 IO latencies: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, >=2000
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