I recently got an Intel 320-series SSD, and I am having difficulty achieving the advertised 38K IOPS for random 4K reads.
fio and my own hacked-together program, I am seeing around 6K IOPS. It's almost like the IO depth size does not matter, and the kernel is trying to fetch one block at a time.
$ cat job [randread] filename=/dev/sdb2 rw=randread size=128m blocksize=4k ioengine=libaio iodepth=64 direct=1 $ sudo fio job randread: (g=0): rw=randread, bs=4K-4K/4K-4K, ioengine=libaio, iodepth=64 Starting 1 process Jobs: 1 (f=1): [r] [100.0% done] [25423K/0K /s] [6207/0 iops] [eta 00m:00s] randread: (groupid=0, jobs=1): err= 0: pid=4678 read : io=131072KB, bw=24852KB/s, iops=6213, runt= 5274msec slat (usec): min=1, max=94, avg= 5.00, stdev= 2.88 clat (usec): min=312, max=13070, avg=10290.25, stdev=1399.78 bw (KB/s) : min=23192, max=24464, per=97.08%, avg=24125.60, stdev=383.70 cpu : usr=15.74%, sys=22.57%, ctx=31642, majf=0, minf=88 IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, >=64=99.8% submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.1%, >=64=0.0% issued r/w: total=32768/0, short=0/0 lat (usec): 500=0.01%, 750=0.01%, 1000=0.03% lat (msec): 2=0.05%, 4=0.10%, 10=20.10%, 20=79.70% Run status group 0 (all jobs): READ: io=131072KB, aggrb=24852KB/s, minb=25448KB/s, maxb=25448KB/s, mint=5274msec, maxt=5274msec Disk stats (read/write): sdb: ios=30453/0, merge=850/0, ticks=319060/0, in_queue=319060, util=98.09%
The system is
Linux 2.6.35-31-generic #63-Ubuntu SMP Mon Nov 28 19:29:10 UTC 2011 x86_64 GNU/Linux.
/dev/sdb2 above is a ~10GB partition on an 80GB SSD.
fio is version 1.38.
Would really appreciate thoughts on what might be wrong.
PS: The partition in the above test (
/dev/sdb2) is aligned on a 4K boundary. Reading from a larger span (size=10g) does not help.