PERC6/i vs. SAS6/iR performance testing?

Matt Cowger matt at cowger.us
Fri Jan 22 18:41:18 CST 2010


I could be wrong, but my understanding is that the perc cards have BB write caches and that the SAS cards do not, which would certainly have a very significant effect in iops.

--M


On Jan 22, 2010, at 4:38 PM, Kaerka Phillips wrote:

> Hello,
> 
> I was wondering if anyone on the linux-poweredge list has done any performance testing of same or similar hardware using the PERC6 vs. the SAS6 controller cards?  I have 7 R805's, two of which have PERC6/i cards installed, and the other 5 have SAS6/iR cards installed.  I've been working on diagnosing a performance problem on two of those with the SAS cards, and have now discovered that every R805 with the SAS cards has similar levels of poor local disk i/o performance.  The R805's with PERC6 cards are similar in performance level to our R905's with PERC6's, and a little better than our 2950's with PERC5's.
> 
> I can provide my stats, but since they're somewhat extensive, the short answer is that the R805's which have PERC6 cards perform in the 16k to 30k i/o per second, depending on write or read type with iozone; but the ones with the SAS cards can barely do 1000 i/o's per second.  These R805's are similar, but not identical though, here is the mix below.  
> 
> All are RHEL5.4, 64bit, and the bottom 3 run kernel-xen, the top two are the standard RHEL5 64bit kernel
> 2x R805's with 2x cpu, 8gb ram, SAS6/iR card, 2x sas 3gbps disks, raid-1 - Avg. 284 i/o per second
> 3x R805's with 2x cpu, 64gb ram, SAS6/iR card, 2x sas 3gbps disks, raid-1 - Avg. 687 i/o per second
> 2x R805's with 2x cpu, 64gb ram, PERC6/i card, 2x sas 3gbps disks, raid-1 - Avg. 26k i/o per second
> 
> I'm hoping that someone else out there has done some other similar performance testing, and can either tell me what I'm doing wrong or also show similar results?  My test methods have been using iozone, dd, and rsync.  (iozone command line:  iozone -s 1m -r 16 -i 0 -i 2 -I -O -t 75)
> 
> Thanks,
> 
> KBP
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