On Sat, May 14, 2011 at 12:07:02PM -0500, ktm@xxxxxxxx wrote: > On Fri, May 13, 2011 at 09:09:41PM +0000, John Rouillard wrote: > > I am adding pgiosim to our testing for new database hardware and I am > > seeing something I don't quite get and I think it's because I am using > > pgiosim incorrectly. > > > > Specs: > > > > OS: centos 5.5 kernel: 2.6.18-194.32.1.el5 > > memory: 96GB > > cpu: 2x Intel(R) Xeon(R) X5690 @ 3.47GHz (6 core, ht enabled) > > disks: WD2003FYYS RE4 > > raid: lsi - 9260-4i with 8 disks in raid 10 configuration > > 1MB stripe size > > raid cache enabled w/ bbu > > disk caches disabled > > filesystem: ext3 created with -E stride=256 > > > > I am seeing really poor (70) iops with pgiosim. According to: > > http://www.tomshardware.com/reviews/2tb-hdd-7200,2430-8.html in the > > database benchmark they are seeing ~170 iops on a single disk for > > these drives. I would expect an 8 disk raid 10 should get better then > > 3x the single disk rate (assuming the data is randomly distributed). > Those drives are 7200 rpm drives which would give you a maximum write > rate of 120/sec at best with the cache disabled. I actually think your > 70/sec is closer to reality and what you should anticipate in real use. > I do not see how they could make 170/sec. Did they strap a jet engine to > the drive. :) Hmm, I stated the disk cache was disabled. I should have said the disk write cache, but it's possible the readhead cache is disabled as well (not quite sure how to tell on the lsi cards). Also there isn't a lot of detail in what the database test mix is and I haven't tried researching the site to see if the spec the exact test. If it included a lot of writes and they were being handled by a cache then that could explain it. However, in my case I have an 8 disk raid 10 with a read only load (in this testing configuration). Shouldn't I expect more iops than a single disk can provide? Maybe pgiosim is hitting some other boundary than just i/o? Also it turns out that pgiosim can only handle 64 files. I haven't checked to see if this is a compile time changable item or not. -- -- rouilj John Rouillard System Administrator Renesys Corporation 603-244-9084 (cell) 603-643-9300 x 111 -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
