On 12/13/2011 01:48 PM, Daniel Fussell wrote: > >> I have turned on the write cache as well as blockdev --setra 16384, >> but it doesn't appear to help much. I did however try to enable the >> write cache and got a little speed increase, but nothing like I >> expected. >> >> Any thoughts on better ways to benchmark this, and also thoughts on >> tuning my 3ware controller? I am using a 32 but version of Linux, >> Hopefully that is enough info to point me in the right direction. >> >> >> --Dallin Jones >> >> /* >> PLUG: http://plug.org, #utah on irc.freenode.net >> Unsubscribe: http://plug.org/mailman/options/plug >> Don't fear the penguin. >> */ >> > Are these SATA, SAS, or Fibrechannel? > > After looking at the array back-end statistics, it appears the array is > doing a write-read/verify since there are as many back-end reads as > writes and my dd process should be generating enough contiguous writes > to ensure full stripe writes. > > Eventually I ran out of ideas and accepted that these "Enterprise" SATA > drives may still be of the 1/4 duty cycle variety, and will not perform > well on writes; especially when the best case write load ends up being a > mixed read/write load anyway. > > If someone else knows of black voodoo magic that improves array > performance, feel free to share. > > Grazie, > ;-Daniel Fussell > > /* > PLUG: http://plug.org, #utah on irc.freenode.net > Unsubscribe: http://plug.org/mailman/options/plug > Don't fear the penguin. > */ I haven't tried this myself, but I came across an article that suggests a type of race condition exists between OS disk caching and RAID controller disk caching. The suggestion was to test one without the other to see if performance improved and then test the inverse condition.
Cooling might also be an issue. The Adaptec cards I have used with passive cooling seem to require a great deal of airflow to remain stable. Symptoms I have witnessed relating to overheating include degraded I/O performance and in extreme cases kernel panics on the RAID controller itself. HTH --Henry /* PLUG: http://plug.org, #utah on irc.freenode.net Unsubscribe: http://plug.org/mailman/options/plug Don't fear the penguin. */
