Only do the root warning once per thread
[fio.git] / HOWTO
CommitLineData
71bfa161
JA
1Table of contents
2-----------------
3
41. Overview
52. How fio works
63. Running fio
74. Job file format
85. Detailed list of parameters
96. Normal output
107. Terse output
11
12
131.0 Overview and history
14------------------------
15fio was originally written to save me the hassle of writing special test
16case programs when I wanted to test a specific workload, either for
17performance reasons or to find/reproduce a bug. The process of writing
18such a test app can be tiresome, especially if you have to do it often.
19Hence I needed a tool that would be able to simulate a given io workload
20without resorting to writing a tailored test case again and again.
21
22A test work load is difficult to define, though. There can be any number
23of processes or threads involved, and they can each be using their own
24way of generating io. You could have someone dirtying large amounts of
25memory in an memory mapped file, or maybe several threads issuing
26reads using asynchronous io. fio needed to be flexible enough to
27simulate both of these cases, and many more.
28
292.0 How fio works
30-----------------
31The first step in getting fio to simulate a desired io workload, is
32writing a job file describing that specific setup. A job file may contain
33any number of threads and/or files - the typical contents of the job file
34is a global section defining shared parameters, and one or more job
35sections describing the jobs involved. When run, fio parses this file
36and sets everything up as described. If we break down a job from top to
37bottom, it contains the following basic parameters:
38
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.
43
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
46 block sizes.
47
48 IO size How much data are we going to be reading/writing.
49
50 IO engine How do we issue io? We could be memory mapping the
51 file, we could be using regular read/write, we
d0ff85df 52 could be using splice, async io, syslet, or even
71bfa161
JA
53 SG (SCSI generic sg).
54
6c219763 55 IO depth If the io engine is async, how large a queuing
71bfa161
JA
56 depth do we want to maintain?
57
58 IO type Should we be doing buffered io, or direct/raw io?
59
60 Num files How many files are we spreading the workload over.
61
62 Num threads How many threads or processes should we spread
63 this workload over.
64
65The above are the basic parameters defined for a workload, in addition
66there's a multitude of parameters that modify other aspects of how this
67job behaves.
68
69
703.0 Running fio
71---------------
72See the README file for command line parameters, there are only a few
73of them.
74
75Running fio is normally the easiest part - you just give it the job file
76(or job files) as parameters:
77
78$ fio job_file
79
80and it will start doing what the job_file tells it to do. You can give
81more than one job file on the command line, fio will serialize the running
82of those files. Internally that is the same as using the 'stonewall'
83parameter described the the parameter section.
84
b4692828
JA
85If the job file contains only one job, you may as well just give the
86parameters on the command line. The command line parameters are identical
87to the job parameters, with a few extra that control global parameters
88(see README). For example, for the job file parameter iodepth=2, the
c2b1e753
JA
89mirror command line option would be --iodepth 2 or --iodepth=2. You can
90also 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.
92Command line entries following a --name entry will apply to that job,
93until there are no more entries or a new --name entry is seen. This is
94similar to the job file options, where each option applies to the current
95job until a new [] job entry is seen.
b4692828 96
71bfa161
JA
97fio does not need to run as root, except if the files or devices specified
98in the job section requires that. Some other options may also be restricted,
6c219763 99such as memory locking, io scheduler switching, and decreasing the nice value.
71bfa161
JA
100
101
1024.0 Job file format
103-------------------
104As previously described, fio accepts one or more job files describing
105what it is supposed to do. The job file format is the classic ini file,
106where the names enclosed in [] brackets define the job name. You are free
107to use any ascii name you want, except 'global' which has special meaning.
108A global section sets defaults for the jobs described in that file. A job
109may override a global section parameter, and a job file may even have
110several global sections if so desired. A job is only affected by a global
65db0851
JA
111section residing above it. If the first character in a line is a ';' or a
112'#', the entire line is discarded as a comment.
71bfa161
JA
113
114So lets look at a really simple job file that define to threads, each
115randomly reading from a 128MiB file.
116
117; -- start job file --
118[global]
119rw=randread
120size=128m
121
122[job1]
123
124[job2]
125
126; -- end job file --
127
128As you can see, the job file sections themselves are empty as all the
129described parameters are shared. As no filename= option is given, fio
c2b1e753
JA
130makes up a filename for each of the jobs as it sees fit. On the command
131line, this job would look as follows:
132
133$ fio --name=global --rw=randread --size=128m --name=job1 --name=job2
134
71bfa161
JA
135
136Lets look at an example that have a number of processes writing randomly
137to files.
138
139; -- start job file --
140[random-writers]
141ioengine=libaio
142iodepth=4
143rw=randwrite
144bs=32k
145direct=0
146size=64m
147numjobs=4
148
149; -- end job file --
150
151Here we have no global section, as we only have one job defined anyway.
152We want to use async io here, with a depth of 4 for each file. We also
153increased the buffer size used to 32KiB and define numjobs to 4 to
154fork 4 identical jobs. The result is 4 processes each randomly writing
b4692828
JA
155to their own 64MiB file. Instead of using the above job file, you could
156have given the parameters on the command line. For this case, you would
157specify:
158
159$ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4
71bfa161
JA
160
161fio ships with a few example job files, you can also look there for
162inspiration.
163
164
1655.0 Detailed list of parameters
166-------------------------------
167
168This section describes in details each parameter associated with a job.
169Some parameters take an option of a given type, such as an integer or
170a string. The following types are used:
171
172str String. This is a sequence of alpha characters.
7616cafe 173int Integer. A whole number value, can be negative.
71bfa161
JA
174siint SI integer. A whole number value, which may contain a postfix
175 describing the base of the number. Accepted postfixes are k/m/g,
6c219763 176 meaning kilo, mega, and giga. So if you want to specify 4096,
71bfa161
JA
177 you could either write out '4096' or just give 4k. The postfixes
178 signify base 2 values, so 1024 is 1k and 1024k is 1m and so on.
43159d18
JA
179 If the option accepts an upper and lower range, use a colon ':'
180 or minus '-' to seperate such values. See irange.
71bfa161
JA
181bool Boolean. Usually parsed as an integer, however only defined for
182 true and false (1 and 0).
183irange Integer range with postfix. Allows value range to be given, such
0c9baf91
JA
184 as 1024-4096. A colon may also be used as the seperator, eg
185 1k:4k. If the option allows two sets of ranges, they can be
186 specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see
187 siint.
71bfa161
JA
188
189With the above in mind, here follows the complete list of fio job
190parameters.
191
192name=str ASCII name of the job. This may be used to override the
193 name printed by fio for this job. Otherwise the job
c2b1e753 194 name is used. On the command line this parameter has the
6c219763 195 special purpose of also signaling the start of a new
c2b1e753 196 job.
71bfa161 197
61697c37
JA
198description=str Text description of the job. Doesn't do anything except
199 dump this text description when this job is run. It's
200 not parsed.
201
71bfa161
JA
202directory=str Prefix filenames with this directory. Used to places files
203 in a different location than "./".
204
205filename=str Fio normally makes up a filename based on the job name,
206 thread number, and file number. If you want to share
207 files between threads in a job or several jobs, specify
ed92ac0c
JA
208 a filename for each of them to override the default. If
209 the ioengine used is 'net', the filename is the host and
9f9214f2 210 port to connect to in the format of =host/port. If the
af52b345
JA
211 ioengine is file based, you can specify a number of files
212 by seperating the names with a ':' colon. So if you wanted
213 a job to open /dev/sda and /dev/sdb as the two working files,
66159828
JA
214 you would use filename=/dev/sda:/dev/sdb. '-' is a reserved
215 name, meaning stdin or stdout. Which of the two depends
216 on the read/write direction set.
71bfa161 217
bbf6b540
JA
218opendir=str Tell fio to recursively add any file it can find in this
219 directory and down the file system tree.
220
d3aad8f2 221readwrite=str
71bfa161
JA
222rw=str Type of io pattern. Accepted values are:
223
224 read Sequential reads
225 write Sequential writes
226 randwrite Random writes
227 randread Random reads
228 rw Sequential mixed reads and writes
229 randrw Random mixed reads and writes
230
231 For the mixed io types, the default is to split them 50/50.
232 For certain types of io the result may still be skewed a bit,
211097b2
JA
233 since the speed may be different. It is possible to specify
234 a number of IO's to do before getting a new offset - this
235 is only useful for random IO, where fio would normally
236 generate a new random offset for every IO. If you append
237 eg 8 to randread, you would get a new random offset for
238 every 8 IO's. The result would be a seek for only every 8
239 IO's, instead of for every IO. Use rw=randread:8 to specify
240 that.
71bfa161 241
ee738499
JA
242randrepeat=bool For random IO workloads, seed the generator in a predictable
243 way so that results are repeatable across repetitions.
244
d2f3ac35
JA
245fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
246 on what IO patterns it is likely to issue. Sometimes you
247 want to test specific IO patterns without telling the
248 kernel about it, in which case you can disable this option.
249 If set, fio will use POSIX_FADV_SEQUENTIAL for sequential
250 IO and POSIX_FADV_RANDOM for random IO.
251
7616cafe
JA
252size=siint The total size of file io for this job. Fio will run until
253 this many bytes has been transferred, unless runtime is
254 limited by other options (such as 'runtime', for instance).
255 Unless specific nr_files and filesize options are given,
256 fio will divide this size between the available files
257 specified by the job.
71bfa161 258
9c60ce64
JA
259filesize=siint Individual file sizes. May be a range, in which case fio
260 will select sizes for files at random within the given range
261 and limited to 'size' in total (if that is given). If not
262 given, each created file is the same size.
263
d3aad8f2 264blocksize=siint
f90eff5a
JA
265bs=siint The block size used for the io units. Defaults to 4k. Values
266 can be given for both read and writes. If a single siint is
267 given, it will apply to both. If a second siint is specified
268 after a comma, it will apply to writes only. In other words,
269 the format is either bs=read_and_write or bs=read,write.
270 bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
787f7e95
JA
271 for writes. If you only wish to set the write size, you
272 can do so by passing an empty read size - bs=,8k will set
273 8k for writes and leave the read default value.
a00735e6 274
d3aad8f2 275blocksize_range=irange
71bfa161
JA
276bsrange=irange Instead of giving a single block size, specify a range
277 and fio will mix the issued io block sizes. The issued
278 io unit will always be a multiple of the minimum value
f90eff5a
JA
279 given (also see bs_unaligned). Applies to both reads and
280 writes, however a second range can be given after a comma.
281 See bs=.
a00735e6 282
d3aad8f2 283blocksize_unaligned
690adba3
JA
284bs_unaligned If this option is given, any byte size value within bsrange
285 may be used as a block range. This typically wont work with
286 direct IO, as that normally requires sector alignment.
71bfa161 287
e9459e5a
JA
288zero_buffers If this option is given, fio will init the IO buffers to
289 all zeroes. The default is to fill them with random data.
290
71bfa161
JA
291nrfiles=int Number of files to use for this job. Defaults to 1.
292
390b1537
JA
293openfiles=int Number of files to keep open at the same time. Defaults to
294 the same as nrfiles, can be set smaller to limit the number
295 simultaneous opens.
296
5af1c6f3
JA
297file_service_type=str Defines how fio decides which file from a job to
298 service next. The following types are defined:
299
300 random Just choose a file at random.
301
302 roundrobin Round robin over open files. This
303 is the default.
304
1907dbc6
JA
305 The string can have a number appended, indicating how
306 often to switch to a new file. So if option random:4 is
307 given, fio will switch to a new random file after 4 ios
308 have been issued.
309
71bfa161
JA
310ioengine=str Defines how the job issues io to the file. The following
311 types are defined:
312
313 sync Basic read(2) or write(2) io. lseek(2) is
314 used to position the io location.
315
316 libaio Linux native asynchronous io.
317
318 posixaio glibc posix asynchronous io.
319
320 mmap File is memory mapped and data copied
321 to/from using memcpy(3).
322
323 splice splice(2) is used to transfer the data and
324 vmsplice(2) to transfer data from user
325 space to the kernel.
326
d0ff85df
JA
327 syslet-rw Use the syslet system calls to make
328 regular read/write async.
329
71bfa161 330 sg SCSI generic sg v3 io. May either be
6c219763 331 synchronous using the SG_IO ioctl, or if
71bfa161
JA
332 the target is an sg character device
333 we use read(2) and write(2) for asynchronous
334 io.
335
a94ea28b
JA
336 null Doesn't transfer any data, just pretends
337 to. This is mainly used to exercise fio
338 itself and for debugging/testing purposes.
339
ed92ac0c
JA
340 net Transfer over the network to given host:port.
341 'filename' must be set appropriately to
9f9214f2 342 filename=host/port regardless of send
ed92ac0c
JA
343 or receive, if the latter only the port
344 argument is used.
345
9cce02e8
JA
346 netsplice Like net, but uses splice/vmsplice to
347 map data and send/receive.
348
ba0fbe10
JA
349 cpu Doesn't transfer any data, but burns CPU
350 cycles according to the cpuload= and
351 cpucycle= options. Setting cpuload=85
352 will cause that job to do nothing but burn
353 85% of the CPU.
354
e9a1806f
JA
355 guasi The GUASI IO engine is the Generic Userspace
356 Asyncronous Syscall Interface approach
357 to async IO. See
358
359 http://www.xmailserver.org/guasi-lib.html
360
361 for more info on GUASI.
362
8a7bd877
JA
363 external Prefix to specify loading an external
364 IO engine object file. Append the engine
365 filename, eg ioengine=external:/tmp/foo.o
366 to load ioengine foo.o in /tmp.
367
71bfa161
JA
368iodepth=int This defines how many io units to keep in flight against
369 the file. The default is 1 for each file defined in this
370 job, can be overridden with a larger value for higher
371 concurrency.
372
cb5ab512
JA
373iodepth_batch=int This defines how many pieces of IO to submit at once.
374 It defaults to the same as iodepth, but can be set lower
375 if one so desires.
376
e916b390
JA
377iodepth_low=int The low water mark indicating when to start filling
378 the queue again. Defaults to the same as iodepth, meaning
379 that fio will attempt to keep the queue full at all times.
380 If iodepth is set to eg 16 and iodepth_low is set to 4, then
381 after fio has filled the queue of 16 requests, it will let
382 the depth drain down to 4 before starting to fill it again.
383
71bfa161 384direct=bool If value is true, use non-buffered io. This is usually
76a43db4
JA
385 O_DIRECT.
386
387buffered=bool If value is true, use buffered io. This is the opposite
388 of the 'direct' option. Defaults to true.
71bfa161
JA
389
390offset=siint Start io at the given offset in the file. The data before
391 the given offset will not be touched. This effectively
392 caps the file size at real_size - offset.
393
394fsync=int If writing to a file, issue a sync of the dirty data
395 for every number of blocks given. For example, if you give
396 32 as a parameter, fio will sync the file for every 32
397 writes issued. If fio is using non-buffered io, we may
398 not sync the file. The exception is the sg io engine, which
6c219763 399 synchronizes the disk cache anyway.
71bfa161
JA
400
401overwrite=bool If writing to a file, setup the file first and do overwrites.
402
403end_fsync=bool If true, fsync file contents when the job exits.
404
ebb1415f
JA
405fsync_on_close=bool If true, fio will fsync() a dirty file on close.
406 This differs from end_fsync in that it will happen on every
407 file close, not just at the end of the job.
408
6c219763 409rwmixcycle=int Value in milliseconds describing how often to switch between
71bfa161
JA
410 reads and writes for a mixed workload. The default is
411 500 msecs.
412
413rwmixread=int How large a percentage of the mix should be reads.
414
415rwmixwrite=int How large a percentage of the mix should be writes. If both
416 rwmixread and rwmixwrite is given and the values do not add
417 up to 100%, the latter of the two will be used to override
418 the first.
419
bb8895e0
JA
420norandommap Normally fio will cover every block of the file when doing
421 random IO. If this option is given, fio will just get a
422 new random offset without looking at past io history. This
423 means that some blocks may not be read or written, and that
424 some blocks may be read/written more than once. This option
7616cafe
JA
425 is mutually exclusive with verify= for that reason, since
426 fio doesn't track potential block rewrites which may alter
427 the calculated checksum for that block.
bb8895e0 428
71bfa161
JA
429nice=int Run the job with the given nice value. See man nice(2).
430
431prio=int Set the io priority value of this job. Linux limits us to
432 a positive value between 0 and 7, with 0 being the highest.
433 See man ionice(1).
434
435prioclass=int Set the io priority class. See man ionice(1).
436
437thinktime=int Stall the job x microseconds after an io has completed before
438 issuing the next. May be used to simulate processing being
48097d5c
JA
439 done by an application. See thinktime_blocks and
440 thinktime_spin.
441
442thinktime_spin=int
443 Only valid if thinktime is set - pretend to spend CPU time
444 doing something with the data received, before falling back
445 to sleeping for the rest of the period specified by
446 thinktime.
9c1f7434
JA
447
448thinktime_blocks
449 Only valid if thinktime is set - control how many blocks
450 to issue, before waiting 'thinktime' usecs. If not set,
451 defaults to 1 which will make fio wait 'thinktime' usecs
452 after every block.
71bfa161
JA
453
454rate=int Cap the bandwidth used by this job to this number of KiB/sec.
455
456ratemin=int Tell fio to do whatever it can to maintain at least this
4e991c23
JA
457 bandwidth. Failing to meet this requirement, will cause
458 the job to exit.
459
460rate_iops=int Cap the bandwidth to this number of IOPS. Basically the same
461 as rate, just specified independently of bandwidth. If the
462 job is given a block size range instead of a fixed value,
463 the smallest block size is used as the metric.
464
465rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
466 the job to exit.
71bfa161
JA
467
468ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
6c219763 469 of milliseconds.
71bfa161
JA
470
471cpumask=int Set the CPU affinity of this job. The parameter given is a
a08bc17f
JA
472 bitmask of allowed CPU's the job may run on. So if you want
473 the allowed CPUs to be 1 and 5, you would pass the decimal
474 value of (1 << 1 | 1 << 5), or 34. See man
7dbb6eba
JA
475 sched_setaffinity(2). This may not work on all supported
476 operating systems or kernel versions.
71bfa161 477
d2e268b0
JA
478cpus_allowed=str Controls the same options as cpumask, but it allows a text
479 setting of the permitted CPUs instead. So to use CPUs 1 and
480 5, you would specify cpus_allowed=1,5.
481
71bfa161
JA
482startdelay=int Start this job the specified number of seconds after fio
483 has started. Only useful if the job file contains several
484 jobs, and you want to delay starting some jobs to a certain
485 time.
486
03b74b3e 487runtime=int Tell fio to terminate processing after the specified number
71bfa161
JA
488 of seconds. It can be quite hard to determine for how long
489 a specified job will run, so this parameter is handy to
490 cap the total runtime to a given time.
491
cf4464ca
JA
492time_based If set, fio will run for the duration of the runtime
493 specified even if the file(s) are completey read or
494 written. It will simply loop over the same workload
495 as many times as the runtime allows.
496
71bfa161
JA
497invalidate=bool Invalidate the buffer/page cache parts for this file prior
498 to starting io. Defaults to true.
499
500sync=bool Use sync io for buffered writes. For the majority of the
501 io engines, this means using O_SYNC.
502
d3aad8f2 503iomem=str
71bfa161
JA
504mem=str Fio can use various types of memory as the io unit buffer.
505 The allowed values are:
506
507 malloc Use memory from malloc(3) as the buffers.
508
509 shm Use shared memory as the buffers. Allocated
510 through shmget(2).
511
74b025b0
JA
512 shmhuge Same as shm, but use huge pages as backing.
513
313cb206
JA
514 mmap Use mmap to allocate buffers. May either be
515 anonymous memory, or can be file backed if
516 a filename is given after the option. The
517 format is mem=mmap:/path/to/file.
71bfa161 518
d0bdaf49
JA
519 mmaphuge Use a memory mapped huge file as the buffer
520 backing. Append filename after mmaphuge, ala
521 mem=mmaphuge:/hugetlbfs/file
522
71bfa161 523 The area allocated is a function of the maximum allowed
5394ae5f
JA
524 bs size for the job, multiplied by the io depth given. Note
525 that for shmhuge and mmaphuge to work, the system must have
526 free huge pages allocated. This can normally be checked
527 and set by reading/writing /proc/sys/vm/nr_hugepages on a
528 Linux system. Fio assumes a huge page is 4MiB in size. So
529 to calculate the number of huge pages you need for a given
530 job file, add up the io depth of all jobs (normally one unless
531 iodepth= is used) and multiply by the maximum bs set. Then
532 divide that number by the huge page size. You can see the
533 size of the huge pages in /proc/meminfo. If no huge pages
534 are allocated by having a non-zero number in nr_hugepages,
56bb17f2 535 using mmaphuge or shmhuge will fail. Also see hugepage-size.
5394ae5f
JA
536
537 mmaphuge also needs to have hugetlbfs mounted and the file
538 location should point there. So if it's mounted in /huge,
539 you would use mem=mmaphuge:/huge/somefile.
71bfa161 540
56bb17f2
JA
541hugepage-size=siint
542 Defines the size of a huge page. Must at least be equal
543 to the system setting, see /proc/meminfo. Defaults to 4MiB.
c51074e7
JA
544 Should probably always be a multiple of megabytes, so using
545 hugepage-size=Xm is the preferred way to set this to avoid
546 setting a non-pow-2 bad value.
56bb17f2 547
71bfa161
JA
548exitall When one job finishes, terminate the rest. The default is
549 to wait for each job to finish, sometimes that is not the
550 desired action.
551
552bwavgtime=int Average the calculated bandwidth over the given time. Value
6c219763 553 is specified in milliseconds.
71bfa161
JA
554
555create_serialize=bool If true, serialize the file creating for the jobs.
556 This may be handy to avoid interleaving of data
557 files, which may greatly depend on the filesystem
558 used and even the number of processors in the system.
559
560create_fsync=bool fsync the data file after creation. This is the
561 default.
562
e545a6ce
JA
563unlink=bool Unlink the job files when done. Not the default, as repeated
564 runs of that job would then waste time recreating the fileset
565 again and again.
71bfa161
JA
566
567loops=int Run the specified number of iterations of this job. Used
568 to repeat the same workload a given number of times. Defaults
569 to 1.
570
571verify=str If writing to a file, fio can verify the file contents
572 after each iteration of the job. The allowed values are:
573
574 md5 Use an md5 sum of the data area and store
575 it in the header of each block.
576
577 crc32 Use a crc32 sum of the data area and store
578 it in the header of each block.
579
36690c9b
JA
580 null Only pretend to verify. Useful for testing
581 internals with ioengine=null, not for much
582 else.
583
6c219763 584 This option can be used for repeated burn-in tests of a
71bfa161
JA
585 system to make sure that the written data is also
586 correctly read back.
587
160b966d
JA
588verifysort=bool If set, fio will sort written verify blocks when it deems
589 it faster to read them back in a sorted manner. This is
590 often the case when overwriting an existing file, since
591 the blocks are already laid out in the file system. You
592 can ignore this option unless doing huge amounts of really
593 fast IO where the red-black tree sorting CPU time becomes
594 significant.
595
71bfa161
JA
596stonewall Wait for preceeding jobs in the job file to exit, before
597 starting this one. Can be used to insert serialization
b3d62a75
JA
598 points in the job file. A stone wall also implies starting
599 a new reporting group.
600
601new_group Start a new reporting group. If this option isn't given,
602 jobs in a file will be part of the same reporting group
603 unless seperated by a stone wall (or if it's a group
604 by itself, with the numjobs option).
71bfa161
JA
605
606numjobs=int Create the specified number of clones of this job. May be
607 used to setup a larger number of threads/processes doing
fa28c85a
JA
608 the same thing. We regard that grouping of jobs as a
609 specific group.
610
611group_reporting If 'numjobs' is set, it may be interesting to display
612 statistics for the group as a whole instead of for each
613 individual job. This is especially true of 'numjobs' is
614 large, looking at individual thread/process output quickly
615 becomes unwieldy. If 'group_reporting' is specified, fio
616 will show the final report per-group instead of per-job.
71bfa161
JA
617
618thread fio defaults to forking jobs, however if this option is
619 given, fio will use pthread_create(3) to create threads
620 instead.
621
622zonesize=siint Divide a file into zones of the specified size. See zoneskip.
623
624zoneskip=siint Skip the specified number of bytes when zonesize data has
625 been read. The two zone options can be used to only do
626 io on zones of a file.
627
076efc7c
JA
628write_iolog=str Write the issued io patterns to the specified file. See
629 read_iolog.
71bfa161 630
076efc7c 631read_iolog=str Open an iolog with the specified file name and replay the
71bfa161 632 io patterns it contains. This can be used to store a
6df8adaa
JA
633 workload and replay it sometime later. The iolog given
634 may also be a blktrace binary file, which allows fio
635 to replay a workload captured by blktrace. See blktrace
636 for how to capture such logging data. For blktrace replay,
637 the file needs to be turned into a blkparse binary data
638 file first (blktrace <device> -d file_for_fio.bin).
71bfa161
JA
639
640write_bw_log If given, write a bandwidth log of the jobs in this job
641 file. Can be used to store data of the bandwidth of the
e0da9bc2
JA
642 jobs in their lifetime. The included fio_generate_plots
643 script uses gnuplot to turn these text files into nice
644 graphs.
71bfa161
JA
645
646write_lat_log Same as write_bw_log, except that this option stores io
647 completion latencies instead.
648
649lockmem=siint Pin down the specified amount of memory with mlock(2). Can
650 potentially be used instead of removing memory or booting
651 with less memory to simulate a smaller amount of memory.
652
653exec_prerun=str Before running this job, issue the command specified
654 through system(3).
655
656exec_postrun=str After the job completes, issue the command specified
657 though system(3).
658
659ioscheduler=str Attempt to switch the device hosting the file to the specified
660 io scheduler before running.
661
662cpuload=int If the job is a CPU cycle eater, attempt to use the specified
663 percentage of CPU cycles.
664
665cpuchunks=int If the job is a CPU cycle eater, split the load into
6c219763 666 cycles of the given time. In milliseconds.
71bfa161 667
0a839f30
JA
668disk_util=bool Generate disk utilization statistics, if the platform
669 supports it. Defaults to on.
670
71bfa161
JA
671
6726.0 Interpreting the output
673---------------------------
674
675fio spits out a lot of output. While running, fio will display the
676status of the jobs created. An example of that would be:
677
73c8b082 678Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
71bfa161
JA
679
680The characters inside the square brackets denote the current status of
681each thread. The possible values (in typical life cycle order) are:
682
683Idle Run
684---- ---
685P Thread setup, but not started.
686C Thread created.
687I Thread initialized, waiting.
688 R Running, doing sequential reads.
689 r Running, doing random reads.
690 W Running, doing sequential writes.
691 w Running, doing random writes.
692 M Running, doing mixed sequential reads/writes.
693 m Running, doing mixed random reads/writes.
694 F Running, currently waiting for fsync()
695V Running, doing verification of written data.
696E Thread exited, not reaped by main thread yet.
697_ Thread reaped.
698
699The other values are fairly self explanatory - number of threads
c9f60304
JA
700currently running and doing io, rate of io since last check (read speed
701listed first, then write speed), and the estimated completion percentage
702and time for the running group. It's impossible to estimate runtime of
703the following groups (if any).
71bfa161
JA
704
705When fio is done (or interrupted by ctrl-c), it will show the data for
706each thread, group of threads, and disks in that order. For each data
707direction, the output looks like:
708
709Client1 (g=0): err= 0:
710 write: io= 32MiB, bw= 666KiB/s, runt= 50320msec
6104ddb6
JA
711 slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92
712 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82
713 bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
71bfa161 714 cpu : usr=1.49%, sys=0.25%, ctx=7969
71619dc2 715 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
30061b97 716 issued r/w: total=0/32768, short=0/0
8abdce66
JA
717 lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
718 lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%
71bfa161
JA
719
720The client number is printed, along with the group id and error of that
721thread. Below is the io statistics, here for writes. In the order listed,
722they denote:
723
724io= Number of megabytes io performed
725bw= Average bandwidth rate
726runt= The runtime of that thread
72fbda2a 727 slat= Submission latency (avg being the average, stdev being the
71bfa161
JA
728 standard deviation). This is the time it took to submit
729 the io. For sync io, the slat is really the completion
8a35c71e
JA
730 latency, since queue/complete is one operation there. This
731 value can be in miliseconds or microseconds, fio will choose
732 the most appropriate base and print that. In the example
733 above, miliseconds is the best scale.
71bfa161
JA
734 clat= Completion latency. Same names as slat, this denotes the
735 time from submission to completion of the io pieces. For
736 sync io, clat will usually be equal (or very close) to 0,
737 as the time from submit to complete is basically just
738 CPU time (io has already been done, see slat explanation).
739 bw= Bandwidth. Same names as the xlat stats, but also includes
740 an approximate percentage of total aggregate bandwidth
741 this thread received in this group. This last value is
742 only really useful if the threads in this group are on the
743 same disk, since they are then competing for disk access.
744cpu= CPU usage. User and system time, along with the number
745 of context switches this thread went through.
71619dc2
JA
746IO depths= The distribution of io depths over the job life time. The
747 numbers are divided into powers of 2, so for example the
748 16= entries includes depths up to that value but higher
749 than the previous entry. In other words, it covers the
750 range from 16 to 31.
30061b97
JA
751IO issued= The number of read/write requests issued, and how many
752 of them were short.
ec118304
JA
753IO latencies= The distribution of IO completion latencies. This is the
754 time from when IO leaves fio and when it gets completed.
755 The numbers follow the same pattern as the IO depths,
756 meaning that 2=1.6% means that 1.6% of the IO completed
8abdce66
JA
757 within 2 msecs, 20=12.8% means that 12.8% of the IO
758 took more than 10 msecs, but less than (or equal to) 20 msecs.
71bfa161
JA
759
760After each client has been listed, the group statistics are printed. They
761will look like this:
762
763Run status group 0 (all jobs):
764 READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
765 WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
766
767For each data direction, it prints:
768
769io= Number of megabytes io performed.
770aggrb= Aggregate bandwidth of threads in this group.
771minb= The minimum average bandwidth a thread saw.
772maxb= The maximum average bandwidth a thread saw.
773mint= The smallest runtime of the threads in that group.
774maxt= The longest runtime of the threads in that group.
775
776And finally, the disk statistics are printed. They will look like this:
777
778Disk stats (read/write):
779 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
780
781Each value is printed for both reads and writes, with reads first. The
782numbers denote:
783
784ios= Number of ios performed by all groups.
785merge= Number of merges io the io scheduler.
786ticks= Number of ticks we kept the disk busy.
787io_queue= Total time spent in the disk queue.
788util= The disk utilization. A value of 100% means we kept the disk
789 busy constantly, 50% would be a disk idling half of the time.
790
791
7927.0 Terse output
793----------------
794
795For scripted usage where you typically want to generate tables or graphs
6af019c9 796of the results, fio can output the results in a semicolon separated format.
71bfa161
JA
797The format is one long line of values, such as:
798
6af019c9
JA
799client1;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%
800;0.0%;0.0%;0.0%;0.0%;0.0%
71bfa161
JA
801
802Split up, the format is as follows:
803
804 jobname, groupid, error
805 READ status:
806 KiB IO, bandwidth (KiB/sec), runtime (msec)
807 Submission latency: min, max, mean, deviation
808 Completion latency: min, max, mean, deviation
6c219763 809 Bw: min, max, aggregate percentage of total, mean, deviation
71bfa161
JA
810 WRITE status:
811 KiB IO, bandwidth (KiB/sec), runtime (msec)
812 Submission latency: min, max, mean, deviation
813 Completion latency: min, max, mean, deviation
6c219763 814 Bw: min, max, aggregate percentage of total, mean, deviation
71bfa161 815 CPU usage: user, system, context switches
2270890c
JA
816 IO depths: <=1, 2, 4, 8, 16, 32, >=64
817 IO latencies: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, >=2000
818 Text description
71bfa161 819