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 128MB 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 32KB and define numjobs to 4 to
154 fork 4 identical jobs. The result is 4 processes each randomly writing
155 to their own 64MB 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 4.1 Environment variables
162 -------------------------
164 fio also supports environment variable expansion in job files. Any
165 substring of the form "${VARNAME}" as part of an option value (in other
166 words, on the right of the `='), will be expanded to the value of the
167 environment variable called VARNAME. If no such environment variable
168 is defined, or VARNAME is the empty string, the empty string will be
171 As an example, let's look at a sample fio invocation and job file:
173 $ SIZE=64m NUMJOBS=4 fio jobfile.fio
175 ; -- start job file --
182 This will expand to the following equivalent job file at runtime:
184 ; -- start job file --
191 fio ships with a few example job files, you can also look there for
194 4.2 Reserved keywords
195 ---------------------
197 Additionally, fio has a set of reserved keywords that will be replaced
198 internally with the appropriate value. Those keywords are:
200 $pagesize The architecture page size of the running system
201 $mb_memory Megabytes of total memory in the system
202 $ncpus Number of online available CPUs
204 These can be used on the command line or in the job file, and will be
205 automatically substituted with the current system values when the job
206 is run. Simple math is also supported on these keywords, so you can
207 perform actions like:
211 and get that properly expanded to 8 times the size of memory in the
215 5.0 Detailed list of parameters
216 -------------------------------
218 This section describes in details each parameter associated with a job.
219 Some parameters take an option of a given type, such as an integer or
220 a string. The following types are used:
222 str String. This is a sequence of alpha characters.
223 time Integer with possible time suffix. In seconds unless otherwise
224 specified, use eg 10m for 10 minutes. Accepts s/m/h for seconds,
226 int SI integer. A whole number value, which may contain a suffix
227 describing the base of the number. Accepted suffixes are k/m/g/t/p,
228 meaning kilo, mega, giga, tera, and peta. The suffix is not case
229 sensitive, and you may also include trailing 'b' (eg 'kb' is the same
230 as 'k'). So if you want to specify 4096, you could either write
231 out '4096' or just give 4k. The suffixes signify base 2 values, so
232 1024 is 1k and 1024k is 1m and so on, unless the suffix is explicitly
233 set to a base 10 value using 'kib', 'mib', 'gib', etc. If that is the
234 case, then 1000 is used as the multiplier. This can be handy for
235 disks, since manufacturers generally use base 10 values when listing
236 the capacity of a drive. If the option accepts an upper and lower
237 range, use a colon ':' or minus '-' to separate such values. May also
238 include a prefix to indicate numbers base. If 0x is used, the number
239 is assumed to be hexadecimal. See irange.
240 bool Boolean. Usually parsed as an integer, however only defined for
241 true and false (1 and 0).
242 irange Integer range with suffix. Allows value range to be given, such
243 as 1024-4096. A colon may also be used as the separator, eg
244 1k:4k. If the option allows two sets of ranges, they can be
245 specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see
248 With the above in mind, here follows the complete list of fio job
251 name=str ASCII name of the job. This may be used to override the
252 name printed by fio for this job. Otherwise the job
253 name is used. On the command line this parameter has the
254 special purpose of also signaling the start of a new
257 description=str Text description of the job. Doesn't do anything except
258 dump this text description when this job is run. It's
261 directory=str Prefix filenames with this directory. Used to place files
262 in a different location than "./".
264 filename=str Fio normally makes up a filename based on the job name,
265 thread number, and file number. If you want to share
266 files between threads in a job or several jobs, specify
267 a filename for each of them to override the default. If
268 the ioengine used is 'net', the filename is the host, port,
269 and protocol to use in the format of =host/port/protocol.
270 See ioengine=net for more. If the ioengine is file based, you
271 can specify a number of files by separating the names with a
272 ':' colon. So if you wanted a job to open /dev/sda and /dev/sdb
273 as the two working files, you would use
274 filename=/dev/sda:/dev/sdb. If the wanted filename does need to
275 include a colon, then escape that with a '\' character. For
276 instance, if the filename is "/dev/dsk/foo@3,0:c", then you would
277 use filename="/dev/dsk/foo@3,0\:c". '-' is a reserved name,
278 meaning stdin or stdout. Which of the two depends on the read/write
281 opendir=str Tell fio to recursively add any file it can find in this
282 directory and down the file system tree.
284 lockfile=str Fio defaults to not locking any files before it does
285 IO to them. If a file or file descriptor is shared, fio
286 can serialize IO to that file to make the end result
287 consistent. This is usual for emulating real workloads that
288 share files. The lock modes are:
290 none No locking. The default.
291 exclusive Only one thread/process may do IO,
292 excluding all others.
293 readwrite Read-write locking on the file. Many
294 readers may access the file at the
295 same time, but writes get exclusive
298 The option may be post-fixed with a lock batch number. If
299 set, then each thread/process may do that amount of IOs to
300 the file before giving up the lock. Since lock acquisition is
301 expensive, batching the lock/unlocks will speed up IO.
304 rw=str Type of io pattern. Accepted values are:
306 read Sequential reads
307 write Sequential writes
308 randwrite Random writes
309 randread Random reads
310 rw Sequential mixed reads and writes
311 randrw Random mixed reads and writes
313 For the mixed io types, the default is to split them 50/50.
314 For certain types of io the result may still be skewed a bit,
315 since the speed may be different. It is possible to specify
316 a number of IO's to do before getting a new offset, this is
317 one by appending a ':<nr>' to the end of the string given.
318 For a random read, it would look like 'rw=randread:8' for
319 passing in an offset modifier with a value of 8. See the
320 'rw_sequencer' option.
322 rw_sequencer=str If an offset modifier is given by appending a number to
323 the rw=<str> line, then this option controls how that
324 number modifies the IO offset being generated. Accepted
327 sequential Generate sequential offset
328 identical Generate the same offset
330 'sequential' is only useful for random IO, where fio would
331 normally generate a new random offset for every IO. If you
332 append eg 8 to randread, you would get a new random offset for
333 every 8 IO's. The result would be a seek for only every 8
334 IO's, instead of for every IO. Use rw=randread:8 to specify
335 that. As sequential IO is already sequential, setting
336 'sequential' for that would not result in any differences.
337 'identical' behaves in a similar fashion, except it sends
338 the same offset 8 number of times before generating a new
341 kb_base=int The base unit for a kilobyte. The defacto base is 2^10, 1024.
342 Storage manufacturers like to use 10^3 or 1000 as a base
343 ten unit instead, for obvious reasons. Allow values are
344 1024 or 1000, with 1024 being the default.
346 randrepeat=bool For random IO workloads, seed the generator in a predictable
347 way so that results are repeatable across repetitions.
349 fallocate=bool By default, fio will use fallocate() to advise the system
350 of the size of the file we are going to write. This can be
351 turned off with fallocate=0. May not be available on all
354 fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
355 on what IO patterns it is likely to issue. Sometimes you
356 want to test specific IO patterns without telling the
357 kernel about it, in which case you can disable this option.
358 If set, fio will use POSIX_FADV_SEQUENTIAL for sequential
359 IO and POSIX_FADV_RANDOM for random IO.
361 size=int The total size of file io for this job. Fio will run until
362 this many bytes has been transferred, unless runtime is
363 limited by other options (such as 'runtime', for instance).
364 Unless specific nrfiles and filesize options are given,
365 fio will divide this size between the available files
366 specified by the job. If not set, fio will use the full
367 size of the given files or devices. If the the files
368 do not exist, size must be given.
370 filesize=int Individual file sizes. May be a range, in which case fio
371 will select sizes for files at random within the given range
372 and limited to 'size' in total (if that is given). If not
373 given, each created file is the same size.
375 fill_device=bool Sets size to something really large and waits for ENOSPC (no
376 space left on device) as the terminating condition. Only makes
377 sense with sequential write. For a read workload, the mount
378 point will be filled first then IO started on the result.
381 bs=int The block size used for the io units. Defaults to 4k. Values
382 can be given for both read and writes. If a single int is
383 given, it will apply to both. If a second int is specified
384 after a comma, it will apply to writes only. In other words,
385 the format is either bs=read_and_write or bs=read,write.
386 bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
387 for writes. If you only wish to set the write size, you
388 can do so by passing an empty read size - bs=,8k will set
389 8k for writes and leave the read default value.
392 ba=int At what boundary to align random IO offsets. Defaults to
393 the same as 'blocksize' the minimum blocksize given.
394 Minimum alignment is typically 512b for using direct IO,
395 though it usually depends on the hardware block size. This
396 option is mutually exclusive with using a random map for
397 files, so it will turn off that option.
399 blocksize_range=irange
400 bsrange=irange Instead of giving a single block size, specify a range
401 and fio will mix the issued io block sizes. The issued
402 io unit will always be a multiple of the minimum value
403 given (also see bs_unaligned). Applies to both reads and
404 writes, however a second range can be given after a comma.
407 bssplit=str Sometimes you want even finer grained control of the
408 block sizes issued, not just an even split between them.
409 This option allows you to weight various block sizes,
410 so that you are able to define a specific amount of
411 block sizes issued. The format for this option is:
413 bssplit=blocksize/percentage:blocksize/percentage
415 for as many block sizes as needed. So if you want to define
416 a workload that has 50% 64k blocks, 10% 4k blocks, and
417 40% 32k blocks, you would write:
419 bssplit=4k/10:64k/50:32k/40
421 Ordering does not matter. If the percentage is left blank,
422 fio will fill in the remaining values evenly. So a bssplit
423 option like this one:
425 bssplit=4k/50:1k/:32k/
427 would have 50% 4k ios, and 25% 1k and 32k ios. The percentages
428 always add up to 100, if bssplit is given a range that adds
429 up to more, it will error out.
431 bssplit also supports giving separate splits to reads and
432 writes. The format is identical to what bs= accepts. You
433 have to separate the read and write parts with a comma. So
434 if you want a workload that has 50% 2k reads and 50% 4k reads,
435 while having 90% 4k writes and 10% 8k writes, you would
438 bssplit=2k/50:4k/50,4k/90,8k/10
441 bs_unaligned If this option is given, any byte size value within bsrange
442 may be used as a block range. This typically wont work with
443 direct IO, as that normally requires sector alignment.
445 zero_buffers If this option is given, fio will init the IO buffers to
446 all zeroes. The default is to fill them with random data.
448 refill_buffers If this option is given, fio will refill the IO buffers
449 on every submit. The default is to only fill it at init
450 time and reuse that data. Only makes sense if zero_buffers
451 isn't specified, naturally. If data verification is enabled,
452 refill_buffers is also automatically enabled.
454 nrfiles=int Number of files to use for this job. Defaults to 1.
456 openfiles=int Number of files to keep open at the same time. Defaults to
457 the same as nrfiles, can be set smaller to limit the number
460 file_service_type=str Defines how fio decides which file from a job to
461 service next. The following types are defined:
463 random Just choose a file at random.
465 roundrobin Round robin over open files. This
468 sequential Finish one file before moving on to
469 the next. Multiple files can still be
470 open depending on 'openfiles'.
472 The string can have a number appended, indicating how
473 often to switch to a new file. So if option random:4 is
474 given, fio will switch to a new random file after 4 ios
477 ioengine=str Defines how the job issues io to the file. The following
480 sync Basic read(2) or write(2) io. lseek(2) is
481 used to position the io location.
483 psync Basic pread(2) or pwrite(2) io.
485 vsync Basic readv(2) or writev(2) IO.
487 libaio Linux native asynchronous io. Note that Linux
488 may only support queued behaviour with
489 non-buffered IO (set direct=1 or buffered=0).
491 posixaio glibc posix asynchronous io.
493 solarisaio Solaris native asynchronous io.
495 mmap File is memory mapped and data copied
496 to/from using memcpy(3).
498 splice splice(2) is used to transfer the data and
499 vmsplice(2) to transfer data from user
502 syslet-rw Use the syslet system calls to make
503 regular read/write async.
505 sg SCSI generic sg v3 io. May either be
506 synchronous using the SG_IO ioctl, or if
507 the target is an sg character device
508 we use read(2) and write(2) for asynchronous
511 null Doesn't transfer any data, just pretends
512 to. This is mainly used to exercise fio
513 itself and for debugging/testing purposes.
515 net Transfer over the network to given host:port.
516 'filename' must be set appropriately to
517 filename=host/port/protocol regardless of send
518 or receive, if the latter only the port
519 argument is used. 'host' may be an IP address
520 or hostname, port is the port number to be used,
521 and protocol may be 'udp' or 'tcp'. If no
522 protocol is given, TCP is used.
524 netsplice Like net, but uses splice/vmsplice to
525 map data and send/receive.
527 cpuio Doesn't transfer any data, but burns CPU
528 cycles according to the cpuload= and
529 cpucycle= options. Setting cpuload=85
530 will cause that job to do nothing but burn
531 85% of the CPU. In case of SMP machines,
532 use numjobs=<no_of_cpu> to get desired CPU
533 usage, as the cpuload only loads a single
534 CPU at the desired rate.
536 guasi The GUASI IO engine is the Generic Userspace
537 Asyncronous Syscall Interface approach
540 http://www.xmailserver.org/guasi-lib.html
542 for more info on GUASI.
544 external Prefix to specify loading an external
545 IO engine object file. Append the engine
546 filename, eg ioengine=external:/tmp/foo.o
547 to load ioengine foo.o in /tmp.
549 iodepth=int This defines how many io units to keep in flight against
550 the file. The default is 1 for each file defined in this
551 job, can be overridden with a larger value for higher
554 iodepth_batch_submit=int
555 iodepth_batch=int This defines how many pieces of IO to submit at once.
556 It defaults to 1 which means that we submit each IO
557 as soon as it is available, but can be raised to submit
558 bigger batches of IO at the time.
560 iodepth_batch_complete=int This defines how many pieces of IO to retrieve
561 at once. It defaults to 1 which means that we'll ask
562 for a minimum of 1 IO in the retrieval process from
563 the kernel. The IO retrieval will go on until we
564 hit the limit set by iodepth_low. If this variable is
565 set to 0, then fio will always check for completed
566 events before queuing more IO. This helps reduce
567 IO latency, at the cost of more retrieval system calls.
569 iodepth_low=int The low water mark indicating when to start filling
570 the queue again. Defaults to the same as iodepth, meaning
571 that fio will attempt to keep the queue full at all times.
572 If iodepth is set to eg 16 and iodepth_low is set to 4, then
573 after fio has filled the queue of 16 requests, it will let
574 the depth drain down to 4 before starting to fill it again.
576 direct=bool If value is true, use non-buffered io. This is usually
579 buffered=bool If value is true, use buffered io. This is the opposite
580 of the 'direct' option. Defaults to true.
582 offset=int Start io at the given offset in the file. The data before
583 the given offset will not be touched. This effectively
584 caps the file size at real_size - offset.
586 fsync=int If writing to a file, issue a sync of the dirty data
587 for every number of blocks given. For example, if you give
588 32 as a parameter, fio will sync the file for every 32
589 writes issued. If fio is using non-buffered io, we may
590 not sync the file. The exception is the sg io engine, which
591 synchronizes the disk cache anyway.
593 fdatasync=int Like fsync= but uses fdatasync() to only sync data and not
595 In FreeBSD there is no fdatasync(), this falls back to
598 sync_file_range=str:val Use sync_file_range() for every 'val' number of
599 write operations. Fio will track range of writes that
600 have happened since the last sync_file_range() call. 'str'
601 can currently be one or more of:
603 wait_before SYNC_FILE_RANGE_WAIT_BEFORE
604 write SYNC_FILE_RANGE_WRITE
605 wait_after SYNC_FILE_RANGE_WAIT_AFTER
607 So if you do sync_file_range=wait_before,write:8, fio would
608 use SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE for
609 every 8 writes. Also see the sync_file_range(2) man page.
610 This option is Linux specific.
612 overwrite=bool If true, writes to a file will always overwrite existing
613 data. If the file doesn't already exist, it will be
614 created before the write phase begins. If the file exists
615 and is large enough for the specified write phase, nothing
618 end_fsync=bool If true, fsync file contents when the job exits.
620 fsync_on_close=bool If true, fio will fsync() a dirty file on close.
621 This differs from end_fsync in that it will happen on every
622 file close, not just at the end of the job.
624 rwmixread=int How large a percentage of the mix should be reads.
626 rwmixwrite=int How large a percentage of the mix should be writes. If both
627 rwmixread and rwmixwrite is given and the values do not add
628 up to 100%, the latter of the two will be used to override
629 the first. This may interfere with a given rate setting,
630 if fio is asked to limit reads or writes to a certain rate.
631 If that is the case, then the distribution may be skewed.
633 norandommap Normally fio will cover every block of the file when doing
634 random IO. If this option is given, fio will just get a
635 new random offset without looking at past io history. This
636 means that some blocks may not be read or written, and that
637 some blocks may be read/written more than once. This option
638 is mutually exclusive with verify= if and only if multiple
639 blocksizes (via bsrange=) are used, since fio only tracks
640 complete rewrites of blocks.
642 softrandommap See norandommap. If fio runs with the random block map enabled
643 and it fails to allocate the map, if this option is set it
644 will continue without a random block map. As coverage will
645 not be as complete as with random maps, this option is
648 nice=int Run the job with the given nice value. See man nice(2).
650 prio=int Set the io priority value of this job. Linux limits us to
651 a positive value between 0 and 7, with 0 being the highest.
654 prioclass=int Set the io priority class. See man ionice(1).
656 thinktime=int Stall the job x microseconds after an io has completed before
657 issuing the next. May be used to simulate processing being
658 done by an application. See thinktime_blocks and
662 Only valid if thinktime is set - pretend to spend CPU time
663 doing something with the data received, before falling back
664 to sleeping for the rest of the period specified by
668 Only valid if thinktime is set - control how many blocks
669 to issue, before waiting 'thinktime' usecs. If not set,
670 defaults to 1 which will make fio wait 'thinktime' usecs
673 rate=int Cap the bandwidth used by this job. The number is in bytes/sec,
674 the normal suffix rules apply. You can use rate=500k to limit
675 reads and writes to 500k each, or you can specify read and
676 writes separately. Using rate=1m,500k would limit reads to
677 1MB/sec and writes to 500KB/sec. Capping only reads or
678 writes can be done with rate=,500k or rate=500k,. The former
679 will only limit writes (to 500KB/sec), the latter will only
682 ratemin=int Tell fio to do whatever it can to maintain at least this
683 bandwidth. Failing to meet this requirement, will cause
684 the job to exit. The same format as rate is used for
685 read vs write separation.
687 rate_iops=int Cap the bandwidth to this number of IOPS. Basically the same
688 as rate, just specified independently of bandwidth. If the
689 job is given a block size range instead of a fixed value,
690 the smallest block size is used as the metric. The same format
691 as rate is used for read vs write seperation.
693 rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
694 the job to exit. The same format as rate is used for read vs
697 ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
700 cpumask=int Set the CPU affinity of this job. The parameter given is a
701 bitmask of allowed CPU's the job may run on. So if you want
702 the allowed CPUs to be 1 and 5, you would pass the decimal
703 value of (1 << 1 | 1 << 5), or 34. See man
704 sched_setaffinity(2). This may not work on all supported
705 operating systems or kernel versions. This option doesn't
706 work well for a higher CPU count than what you can store in
707 an integer mask, so it can only control cpus 1-32. For
708 boxes with larger CPU counts, use cpus_allowed.
710 cpus_allowed=str Controls the same options as cpumask, but it allows a text
711 setting of the permitted CPUs instead. So to use CPUs 1 and
712 5, you would specify cpus_allowed=1,5. This options also
713 allows a range of CPUs. Say you wanted a binding to CPUs
714 1, 5, and 8-15, you would set cpus_allowed=1,5,8-15.
716 startdelay=time Start this job the specified number of seconds after fio
717 has started. Only useful if the job file contains several
718 jobs, and you want to delay starting some jobs to a certain
721 runtime=time Tell fio to terminate processing after the specified number
722 of seconds. It can be quite hard to determine for how long
723 a specified job will run, so this parameter is handy to
724 cap the total runtime to a given time.
726 time_based If set, fio will run for the duration of the runtime
727 specified even if the file(s) are completely read or
728 written. It will simply loop over the same workload
729 as many times as the runtime allows.
731 ramp_time=time If set, fio will run the specified workload for this amount
732 of time before logging any performance numbers. Useful for
733 letting performance settle before logging results, thus
734 minimizing the runtime required for stable results. Note
735 that the ramp_time is considered lead in time for a job,
736 thus it will increase the total runtime if a special timeout
737 or runtime is specified.
739 invalidate=bool Invalidate the buffer/page cache parts for this file prior
740 to starting io. Defaults to true.
742 sync=bool Use sync io for buffered writes. For the majority of the
743 io engines, this means using O_SYNC.
746 mem=str Fio can use various types of memory as the io unit buffer.
747 The allowed values are:
749 malloc Use memory from malloc(3) as the buffers.
751 shm Use shared memory as the buffers. Allocated
754 shmhuge Same as shm, but use huge pages as backing.
756 mmap Use mmap to allocate buffers. May either be
757 anonymous memory, or can be file backed if
758 a filename is given after the option. The
759 format is mem=mmap:/path/to/file.
761 mmaphuge Use a memory mapped huge file as the buffer
762 backing. Append filename after mmaphuge, ala
763 mem=mmaphuge:/hugetlbfs/file
765 The area allocated is a function of the maximum allowed
766 bs size for the job, multiplied by the io depth given. Note
767 that for shmhuge and mmaphuge to work, the system must have
768 free huge pages allocated. This can normally be checked
769 and set by reading/writing /proc/sys/vm/nr_hugepages on a
770 Linux system. Fio assumes a huge page is 4MB in size. So
771 to calculate the number of huge pages you need for a given
772 job file, add up the io depth of all jobs (normally one unless
773 iodepth= is used) and multiply by the maximum bs set. Then
774 divide that number by the huge page size. You can see the
775 size of the huge pages in /proc/meminfo. If no huge pages
776 are allocated by having a non-zero number in nr_hugepages,
777 using mmaphuge or shmhuge will fail. Also see hugepage-size.
779 mmaphuge also needs to have hugetlbfs mounted and the file
780 location should point there. So if it's mounted in /huge,
781 you would use mem=mmaphuge:/huge/somefile.
783 iomem_align=int This indiciates the memory alignment of the IO memory buffers.
784 Note that the given alignment is applied to the first IO unit
785 buffer, if using iodepth the alignment of the following buffers
786 are given by the bs used. In other words, if using a bs that is
787 a multiple of the page sized in the system, all buffers will
788 be aligned to this value. If using a bs that is not page
789 aligned, the alignment of subsequent IO memory buffers is the
790 sum of the iomem_align and bs used.
793 Defines the size of a huge page. Must at least be equal
794 to the system setting, see /proc/meminfo. Defaults to 4MB.
795 Should probably always be a multiple of megabytes, so using
796 hugepage-size=Xm is the preferred way to set this to avoid
797 setting a non-pow-2 bad value.
799 exitall When one job finishes, terminate the rest. The default is
800 to wait for each job to finish, sometimes that is not the
803 bwavgtime=int Average the calculated bandwidth over the given time. Value
804 is specified in milliseconds.
806 create_serialize=bool If true, serialize the file creating for the jobs.
807 This may be handy to avoid interleaving of data
808 files, which may greatly depend on the filesystem
809 used and even the number of processors in the system.
811 create_fsync=bool fsync the data file after creation. This is the
814 create_on_open=bool Don't pre-setup the files for IO, just create open()
815 when it's time to do IO to that file.
817 pre_read=bool If this is given, files will be pre-read into memory before
818 starting the given IO operation. This will also clear
819 the 'invalidate' flag, since it is pointless to pre-read
820 and then drop the cache. This will only work for IO engines
821 that are seekable, since they allow you to read the same data
822 multiple times. Thus it will not work on eg network or splice
825 unlink=bool Unlink the job files when done. Not the default, as repeated
826 runs of that job would then waste time recreating the file
829 loops=int Run the specified number of iterations of this job. Used
830 to repeat the same workload a given number of times. Defaults
833 do_verify=bool Run the verify phase after a write phase. Only makes sense if
834 verify is set. Defaults to 1.
836 verify=str If writing to a file, fio can verify the file contents
837 after each iteration of the job. The allowed values are:
839 md5 Use an md5 sum of the data area and store
840 it in the header of each block.
842 crc64 Use an experimental crc64 sum of the data
843 area and store it in the header of each
846 crc32c Use a crc32c sum of the data area and store
847 it in the header of each block.
849 crc32c-intel Use hardware assisted crc32c calcuation
850 provided on SSE4.2 enabled processors. Falls
851 back to regular software crc32c, if not
852 supported by the system.
854 crc32 Use a crc32 sum of the data area and store
855 it in the header of each block.
857 crc16 Use a crc16 sum of the data area and store
858 it in the header of each block.
860 crc7 Use a crc7 sum of the data area and store
861 it in the header of each block.
863 sha512 Use sha512 as the checksum function.
865 sha256 Use sha256 as the checksum function.
867 sha1 Use optimized sha1 as the checksum function.
869 meta Write extra information about each io
870 (timestamp, block number etc.). The block
871 number is verified. See also verify_pattern.
873 null Only pretend to verify. Useful for testing
874 internals with ioengine=null, not for much
877 This option can be used for repeated burn-in tests of a
878 system to make sure that the written data is also
879 correctly read back. If the data direction given is
880 a read or random read, fio will assume that it should
881 verify a previously written file. If the data direction
882 includes any form of write, the verify will be of the
885 verifysort=bool If set, fio will sort written verify blocks when it deems
886 it faster to read them back in a sorted manner. This is
887 often the case when overwriting an existing file, since
888 the blocks are already laid out in the file system. You
889 can ignore this option unless doing huge amounts of really
890 fast IO where the red-black tree sorting CPU time becomes
893 verify_offset=int Swap the verification header with data somewhere else
894 in the block before writing. Its swapped back before
897 verify_interval=int Write the verification header at a finer granularity
898 than the blocksize. It will be written for chunks the
899 size of header_interval. blocksize should divide this
902 verify_pattern=str If set, fio will fill the io buffers with this
903 pattern. Fio defaults to filling with totally random
904 bytes, but sometimes it's interesting to fill with a known
905 pattern for io verification purposes. Depending on the
906 width of the pattern, fio will fill 1/2/3/4 bytes of the
907 buffer at the time(it can be either a decimal or a hex number).
908 The verify_pattern if larger than a 32-bit quantity has to
909 be a hex number that starts with either "0x" or "0X". Use
912 verify_fatal=bool Normally fio will keep checking the entire contents
913 before quitting on a block verification failure. If this
914 option is set, fio will exit the job on the first observed
917 verify_async=int Fio will normally verify IO inline from the submitting
918 thread. This option takes an integer describing how many
919 async offload threads to create for IO verification instead,
920 causing fio to offload the duty of verifying IO contents
921 to one or more separate threads. If using this offload
922 option, even sync IO engines can benefit from using an
923 iodepth setting higher than 1, as it allows them to have
924 IO in flight while verifies are running.
926 verify_async_cpus=str Tell fio to set the given CPU affinity on the
927 async IO verification threads. See cpus_allowed for the
930 verify_backlog=int Fio will normally verify the written contents of a
931 job that utilizes verify once that job has completed. In
932 other words, everything is written then everything is read
933 back and verified. You may want to verify continually
934 instead for a variety of reasons. Fio stores the meta data
935 associated with an IO block in memory, so for large
936 verify workloads, quite a bit of memory would be used up
937 holding this meta data. If this option is enabled, fio
938 will verify the previously written blocks before continuing
941 verify_backlog_batch=int Control how many blocks fio will verify
942 if verify_backlog is set. If not set, will default to
943 the value of verify_backlog (meaning the entire queue
944 is read back and verified).
946 stonewall Wait for preceeding jobs in the job file to exit, before
947 starting this one. Can be used to insert serialization
948 points in the job file. A stone wall also implies starting
949 a new reporting group.
951 new_group Start a new reporting group. If this option isn't given,
952 jobs in a file will be part of the same reporting group
953 unless separated by a stone wall (or if it's a group
954 by itself, with the numjobs option).
956 numjobs=int Create the specified number of clones of this job. May be
957 used to setup a larger number of threads/processes doing
958 the same thing. We regard that grouping of jobs as a
961 group_reporting If 'numjobs' is set, it may be interesting to display
962 statistics for the group as a whole instead of for each
963 individual job. This is especially true of 'numjobs' is
964 large, looking at individual thread/process output quickly
965 becomes unwieldy. If 'group_reporting' is specified, fio
966 will show the final report per-group instead of per-job.
968 thread fio defaults to forking jobs, however if this option is
969 given, fio will use pthread_create(3) to create threads
972 zonesize=int Divide a file into zones of the specified size. See zoneskip.
974 zoneskip=int Skip the specified number of bytes when zonesize data has
975 been read. The two zone options can be used to only do
976 io on zones of a file.
978 write_iolog=str Write the issued io patterns to the specified file. See
981 read_iolog=str Open an iolog with the specified file name and replay the
982 io patterns it contains. This can be used to store a
983 workload and replay it sometime later. The iolog given
984 may also be a blktrace binary file, which allows fio
985 to replay a workload captured by blktrace. See blktrace
986 for how to capture such logging data. For blktrace replay,
987 the file needs to be turned into a blkparse binary data
988 file first (blkparse <device> -o /dev/null -d file_for_fio.bin).
990 write_bw_log=str If given, write a bandwidth log of the jobs in this job
991 file. Can be used to store data of the bandwidth of the
992 jobs in their lifetime. The included fio_generate_plots
993 script uses gnuplot to turn these text files into nice
994 graphs. See write_log_log for behaviour of given
995 filename. For this option, the postfix is _bw.log.
997 write_lat_log=str Same as write_bw_log, except that this option stores io
998 submission, completion, and total latencies instead. If no
999 filename is given with this option, the default filename of
1000 "jobname_type.log" is used. Even if the filename is given,
1001 fio will still append the type of log. So if one specifies
1005 The actual log names will be foo_slat.log, foo_slat.log,
1006 and foo_lat.log. This helps fio_generate_plot fine the logs
1009 lockmem=int Pin down the specified amount of memory with mlock(2). Can
1010 potentially be used instead of removing memory or booting
1011 with less memory to simulate a smaller amount of memory.
1013 exec_prerun=str Before running this job, issue the command specified
1016 exec_postrun=str After the job completes, issue the command specified
1019 ioscheduler=str Attempt to switch the device hosting the file to the specified
1020 io scheduler before running.
1022 cpuload=int If the job is a CPU cycle eater, attempt to use the specified
1023 percentage of CPU cycles.
1025 cpuchunks=int If the job is a CPU cycle eater, split the load into
1026 cycles of the given time. In microseconds.
1028 disk_util=bool Generate disk utilization statistics, if the platform
1029 supports it. Defaults to on.
1031 disable_lat=bool Disable measurements of total latency numbers. Useful
1032 only for cutting back the number of calls to gettimeofday,
1033 as that does impact performance at really high IOPS rates.
1034 Note that to really get rid of a large amount of these
1035 calls, this option must be used with disable_slat and
1038 disable_clat=bool Disable measurements of completion latency numbers. See
1041 disable_slat=bool Disable measurements of submission latency numbers. See
1044 disable_bw=bool Disable measurements of throughput/bandwidth numbers. See
1047 gtod_reduce=bool Enable all of the gettimeofday() reducing options
1048 (disable_clat, disable_slat, disable_bw) plus reduce
1049 precision of the timeout somewhat to really shrink
1050 the gettimeofday() call count. With this option enabled,
1051 we only do about 0.4% of the gtod() calls we would have
1052 done if all time keeping was enabled.
1054 gtod_cpu=int Sometimes it's cheaper to dedicate a single thread of
1055 execution to just getting the current time. Fio (and
1056 databases, for instance) are very intensive on gettimeofday()
1057 calls. With this option, you can set one CPU aside for
1058 doing nothing but logging current time to a shared memory
1059 location. Then the other threads/processes that run IO
1060 workloads need only copy that segment, instead of entering
1061 the kernel with a gettimeofday() call. The CPU set aside
1062 for doing these time calls will be excluded from other
1063 uses. Fio will manually clear it from the CPU mask of other
1066 continue_on_error=bool Normally fio will exit the job on the first observed
1067 failure. If this option is set, fio will continue the job when
1068 there is a 'non-fatal error' (EIO or EILSEQ) until the runtime
1069 is exceeded or the I/O size specified is completed. If this
1070 option is used, there are two more stats that are appended,
1071 the total error count and the first error. The error field
1072 given in the stats is the first error that was hit during the
1075 cgroup=str Add job to this control group. If it doesn't exist, it will
1076 be created. The system must have a mounted cgroup blkio
1077 mount point for this to work. If your system doesn't have it
1078 mounted, you can do so with:
1080 # mount -t cgroup -o blkio none /cgroup
1082 cgroup_weight=int Set the weight of the cgroup to this value. See
1083 the documentation that comes with the kernel, allowed values
1084 are in the range of 100..1000.
1086 cgroup_nodelete=bool Normally fio will delete the cgroups it has created after
1087 the job completion. To override this behavior and to leave
1088 cgroups around after the job completion, set cgroup_nodelete=1.
1089 This can be useful if one wants to inspect various cgroup
1090 files after job completion. Default: false
1092 uid=int Instead of running as the invoking user, set the user ID to
1093 this value before the thread/process does any work.
1095 gid=int Set group ID, see uid.
1097 6.0 Interpreting the output
1098 ---------------------------
1100 fio spits out a lot of output. While running, fio will display the
1101 status of the jobs created. An example of that would be:
1103 Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
1105 The characters inside the square brackets denote the current status of
1106 each thread. The possible values (in typical life cycle order) are:
1110 P Thread setup, but not started.
1112 I Thread initialized, waiting.
1113 p Thread running pre-reading file(s).
1114 R Running, doing sequential reads.
1115 r Running, doing random reads.
1116 W Running, doing sequential writes.
1117 w Running, doing random writes.
1118 M Running, doing mixed sequential reads/writes.
1119 m Running, doing mixed random reads/writes.
1120 F Running, currently waiting for fsync()
1121 V Running, doing verification of written data.
1122 E Thread exited, not reaped by main thread yet.
1125 The other values are fairly self explanatory - number of threads
1126 currently running and doing io, rate of io since last check (read speed
1127 listed first, then write speed), and the estimated completion percentage
1128 and time for the running group. It's impossible to estimate runtime of
1129 the following groups (if any).
1131 When fio is done (or interrupted by ctrl-c), it will show the data for
1132 each thread, group of threads, and disks in that order. For each data
1133 direction, the output looks like:
1135 Client1 (g=0): err= 0:
1136 write: io= 32MB, bw= 666KB/s, runt= 50320msec
1137 slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92
1138 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82
1139 bw (KB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
1140 cpu : usr=1.49%, sys=0.25%, ctx=7969, majf=0, minf=17
1141 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
1142 submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
1143 complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
1144 issued r/w: total=0/32768, short=0/0
1145 lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
1146 lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%
1148 The client number is printed, along with the group id and error of that
1149 thread. Below is the io statistics, here for writes. In the order listed,
1152 io= Number of megabytes io performed
1153 bw= Average bandwidth rate
1154 runt= The runtime of that thread
1155 slat= Submission latency (avg being the average, stdev being the
1156 standard deviation). This is the time it took to submit
1157 the io. For sync io, the slat is really the completion
1158 latency, since queue/complete is one operation there. This
1159 value can be in milliseconds or microseconds, fio will choose
1160 the most appropriate base and print that. In the example
1161 above, milliseconds is the best scale.
1162 clat= Completion latency. Same names as slat, this denotes the
1163 time from submission to completion of the io pieces. For
1164 sync io, clat will usually be equal (or very close) to 0,
1165 as the time from submit to complete is basically just
1166 CPU time (io has already been done, see slat explanation).
1167 bw= Bandwidth. Same names as the xlat stats, but also includes
1168 an approximate percentage of total aggregate bandwidth
1169 this thread received in this group. This last value is
1170 only really useful if the threads in this group are on the
1171 same disk, since they are then competing for disk access.
1172 cpu= CPU usage. User and system time, along with the number
1173 of context switches this thread went through, usage of
1174 system and user time, and finally the number of major
1175 and minor page faults.
1176 IO depths= The distribution of io depths over the job life time. The
1177 numbers are divided into powers of 2, so for example the
1178 16= entries includes depths up to that value but higher
1179 than the previous entry. In other words, it covers the
1180 range from 16 to 31.
1181 IO submit= How many pieces of IO were submitting in a single submit
1182 call. Each entry denotes that amount and below, until
1183 the previous entry - eg, 8=100% mean that we submitted
1184 anywhere in between 5-8 ios per submit call.
1185 IO complete= Like the above submit number, but for completions instead.
1186 IO issued= The number of read/write requests issued, and how many
1188 IO latencies= The distribution of IO completion latencies. This is the
1189 time from when IO leaves fio and when it gets completed.
1190 The numbers follow the same pattern as the IO depths,
1191 meaning that 2=1.6% means that 1.6% of the IO completed
1192 within 2 msecs, 20=12.8% means that 12.8% of the IO
1193 took more than 10 msecs, but less than (or equal to) 20 msecs.
1195 After each client has been listed, the group statistics are printed. They
1196 will look like this:
1198 Run status group 0 (all jobs):
1199 READ: io=64MB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
1200 WRITE: io=64MB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
1202 For each data direction, it prints:
1204 io= Number of megabytes io performed.
1205 aggrb= Aggregate bandwidth of threads in this group.
1206 minb= The minimum average bandwidth a thread saw.
1207 maxb= The maximum average bandwidth a thread saw.
1208 mint= The smallest runtime of the threads in that group.
1209 maxt= The longest runtime of the threads in that group.
1211 And finally, the disk statistics are printed. They will look like this:
1213 Disk stats (read/write):
1214 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
1216 Each value is printed for both reads and writes, with reads first. The
1219 ios= Number of ios performed by all groups.
1220 merge= Number of merges io the io scheduler.
1221 ticks= Number of ticks we kept the disk busy.
1222 io_queue= Total time spent in the disk queue.
1223 util= The disk utilization. A value of 100% means we kept the disk
1224 busy constantly, 50% would be a disk idling half of the time.
1230 For scripted usage where you typically want to generate tables or graphs
1231 of the results, fio can output the results in a semicolon separated format.
1232 The format is one long line of values, such as:
1234 2; 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%
1235 ;0.0%;0.0%;0.0%;0.0%;0.0%
1237 To enable terse output, use the --minimal command line option. The first
1238 value is the version of the terse output format. If the output has to
1239 be changed for some reason, this number will be incremented by 1 to
1240 signify that change.
1242 Split up, the format is as follows:
1244 version, jobname, groupid, error
1246 KB IO, bandwidth (KB/sec), runtime (msec)
1247 Submission latency: min, max, mean, deviation
1248 Completion latency: min, max, mean, deviation
1249 Total latency: min, max, mean, deviation
1250 Bw: min, max, aggregate percentage of total, mean, deviation
1252 KB IO, bandwidth (KB/sec), runtime (msec)
1253 Submission latency: min, max, mean, deviation
1254 Completion latency: min, max, mean, deviation
1255 Total latency: min, max, mean, deviation
1256 Bw: min, max, aggregate percentage of total, mean, deviation
1257 CPU usage: user, system, context switches, major faults, minor faults
1258 IO depths: <=1, 2, 4, 8, 16, 32, >=64
1259 IO latencies: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, >=2000
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