4 fio is a tool that will spawn a number of thread doing a particular
5 type of io action as specified by the user. fio takes a number of
6 global parameters, each inherited by the thread unless otherwise
7 parameters given to them overriding that setting is given.
13 fio resides in a git repo, the canonical place is:
15 git://brick.kernel.dk/data/git/fio.git
17 Snapshots are frequently generated as well and they include the git
18 meta data as well. You can download them here:
20 http://brick.kernel.dk/snaps/
28 -b block size in KiB for each io
29 -t <sec> Runtime in seconds
30 -r For random io, sequence must be repeatable
31 -R <on> If one thread fails to meet rate, quit all
32 -o <on> Use direct IO is 1, buffered if 0
33 -l Generate per-job latency logs
34 -w Generate per-job bandwidth logs
35 -f <file> Read <file> for job descriptions
36 -v Print version information and exit
38 The <jobs> format is as follows:
40 directory=x Use 'x' as the top level directory for storing files
41 rw=x 'x' may be: read, randread, write, or randwrite
42 size=x Set file size to x bytes (x string can include k/m/g)
43 ioengine=x 'x' may be: aio/libaio/linuxaio for Linux aio,
44 posixaio for POSIX aio, sync for regular read/write io,
45 mmap for mmap'ed io, or sgio for direct SG_IO io. The
46 latter only works on Linux on SCSI (or SCSI-like
47 devices, such as usb-storage or sata/libata driven)
49 iodepth=x For async io, allow 'x' ios in flight
50 overwrite=x If 'x', layout a write file first.
51 prio=x Run io at prio X, 0-7 is the kernel allowed range
52 prioclass=x Run io at prio class X
53 bs=x Use 'x' for thread blocksize. May include k/m postfix.
54 bsrange=x-y Mix thread block sizes randomly between x and y. May
55 also include k/m postfix.
56 direct=x 1 for direct IO, 0 for buffered IO
57 thinktime=x "Think" x usec after each io
58 rate=x Throttle rate to x KiB/sec
59 ratemin=x Quit if rate of x KiB/sec can't be met
60 ratecycle=x ratemin averaged over x msecs
61 cpumask=x Only allow job to run on CPUs defined by mask.
62 fsync=x If writing, fsync after every x blocks have been written
63 startdelay=x Start this thread x seconds after startup
64 timeout=x Terminate x seconds after startup
65 offset=x Start io at offset x (x string can include k/m/g)
66 invalidate=x Invalidate page cache for file prior to doing io
67 sync=x Use sync writes if x and writing
68 mem=x If x == malloc, use malloc for buffers. If x == shm,
69 use shm for buffers. If x == mmap, use anon mmap.
70 exitall When one thread quits, terminate the others
71 bwavgtime=x Average bandwidth stats over an x msec window.
72 create_serialize=x If 'x', serialize file creation.
73 create_fsync=x If 'x', run fsync() after file creation.
74 loops=x Run the job 'x' number of times.
75 verify=x If 'x' == md5, use md5 for verifies. If 'x' == crc32,
76 use crc32 for verifies. md5 is 'safer', but crc32 is
77 a lot faster. Only makes sense for writing to a file.
78 stonewall Wait for preceeding jobs to end before running.
79 numjobs=x Create 'x' similar entries for this job
80 thread Use pthreads instead of forked jobs
83 Examples using a job file
84 -------------------------
86 A sample job file doing the same as above would look like this:
96 And fio would be invoked as:
98 $ fio -o1 -s -f file_with_above
100 The second example would look like this:
115 And fio would be invoked as:
117 $ fio -o0 -s -b4096 -f file_with_above
119 'global' is a reserved keyword. When used as the filename, it sets the
120 default options for the threads following that section. It is possible
121 to have more than one global section in the file, as it only affects
124 Also see the examples/ dir for sample job files.
127 Interpreting the output
128 -----------------------
130 fio spits out a lot of output. While running, fio will display the
131 status of the jobs created. An example of that would be:
133 Threads now running: 2 : [ww] [5.73% done]
135 The characters inside the square brackets denote the current status of
136 each thread. The possible values (in typical life cycle order) are:
140 P Thread setup, but not started.
141 C Thread created and running, but not doing anything yet
142 R Running, doing sequential reads.
143 r Running, doing random reads.
144 W Running, doing sequential writes.
145 w Running, doing random writes.
146 V Running, doing verification of written data.
147 E Thread exited, not reaped by main thread yet.
150 The other values are fairly self explanatory - number of thread currently
151 running and doing io, and the estimated completion percentage.
153 When fio is done (or interrupted by ctrl-c), it will show the data for
154 each thread, group of threads, and disks in that order. For each data
155 direction, the output looks like:
157 Client1 (g=0): err= 0:
158 write: io= 32MiB, bw= 666KiB/s, runt= 50320msec
159 slat (msec): min= 0, max= 136, avg= 0.03, dev= 1.92
160 clat (msec): min= 0, max= 631, avg=48.50, dev=86.82
161 bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, dev=681.68
162 cpu : usr=1.49%, sys=0.25%, ctx=7969
164 The client number is printed, along with the group id and error of that
165 thread. Below is the io statistics, here for writes. In the order listed,
168 io= Number of megabytes io performed
169 bw= Average bandwidth rate
170 runt= The runtime of that thread
171 slat= Submission latency (avg being the average, dev being the
172 standard deviation). This is the time it took to submit
173 the io. For sync io, the slat is really the completion
174 latency, since queue/complete is one operation there.
175 clat= Completion latency. Same names as slat, this denotes the
176 time from submission to completion of the io pieces. For
177 sync io, clat will usually be equal (or very close) to 0,
178 as the time from submit to complete is basically just
179 CPU time (io has already been done, see slat explanation).
180 bw= Bandwidth. Same names as the xlat stats, but also includes
181 an approximate percentage of total aggregate bandwidth
182 this thread received in this group. This last value is
183 only really useful if the threads in this group are on the
184 same disk, since they are then competing for disk access.
185 cpu= CPU usage. User and system time, along with the number
186 of context switches this thread went through.
188 After each client has been listed, the group statistics are printed. They
191 Run status group 0 (all jobs):
192 READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
193 WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
195 For each data direction, it prints:
197 io= Number of megabytes io performed.
198 aggrb= Aggregate bandwidth of threads in this group.
199 minb= The minimum average bandwidth a thread saw.
200 maxb= The maximum average bandwidth a thread saw.
201 mint= The minimum runtime of a thread.
202 maxt= The maximum runtime of a thread.
204 And finally, the disk statistics are printed. They will look like this:
206 Disk stats (read/write):
207 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
209 Each value is printed for both reads and writes, with reads first. The
212 ios= Number of ios performed by all groups.
213 merge= Number of merges io the io scheduler.
214 ticks= Number of ticks we kept the disk busy.
215 io_queue= Total time spent in the disk queue.
216 util= The disk utilization. A value of 100% means we kept the disk
217 busy constantly, 50% would be a disk idling half of the time.