On 1/31/2012 2:25 PM, Dave Chinner wrote: > On Tue, Jan 31, 2012 at 02:16:04PM +0000, Brian Candler wrote: >> Here we appear to be limited by real seeks. 225 seeks/sec is still very good > > That number indicates 225 IOs/s, not 225 seeks/s. Yeah, the voice coil actuator and spindle rotation limits the peak random seek rate of good 7.2k drive/controller combos to about 150/s. 15k drives do about 250-300 seeks/s max. Simple tool to test max random seeks/sec for a device: 32bit binary: http://www.hardwarefreak.com/seekerb source: http://www.hardwarefreak.com/seeker_baryluk.c I'm not the author. The original seeker program is single threaded. Baryluk did the thread hacking. Background info: http://www.linuxinsight.com/how_fast_is_your_disk.html Usage: ./seekerb device [threads] Results for a single WD 7.2K drive, no NCQ, deadline elevator: 1 threads Results: 64 seeks/second, 15.416 ms random access time 16 threads Results: 97 seeks/second, 10.285 ms random access time 128 threads Results: 121 seeks/second, 8.208 ms random access time Actual output: $ seekerb /dev/sda 128 Seeker v3.0, 2009-06-17, http://www.linuxinsight.com/how_fast_is_your_disk.html Benchmarking /dev/sda [976773168 blocks, 500107862016 bytes, 465 GB, 476940 MB, 500 GiB, 500107 MiB] [512 logical sector size, 512 physical sector size] [128 threads] Wait 30 seconds............................. Results: 121 seeks/second, 8.208 ms random access time (52614775 < offsets < 499769984475) Targeting array devices (mdraid or hardware, or FC SAN LUN) with lots of spindles, and/or SSDs should yield some interesting results. -- Stan _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
