On Thu, May 21, 2015 at 11:21:49AM +0000, Graeme B. Bell wrote: > > Not using your raid controllers write cache then? Not sure just how > > important that is with SSDs these days, but if you've got a BBU set > > it to "WriteBack". Also change "Cache if Bad BBU" to "No Write Cache > > if Bad BBU" if you do that. > > I did quite a few tests with WB and WT last year. > > - WT should be OK with e.g. Intel SSDs. From memory I saw write > performance gains of about 20-30% with Crucial M500/M550 writes on a > Dell H710 RAID controller. BUT that controller didn't have WT fastpath > though which is absolutely essential to see substantial gains WT. I > expect with WT and a fastpath enabled RAID you'd see much higher > numbers, e.g. 100%+ higher IOPS. > > (So, if you don't have fastpath on your controller, you might as > well plan to leave WB on and just buy cheaper SSD drives rather than > expensive ones - the raid controller will be your choke point for > performance on WT and it's a source of risk). > > - WT with most SSDs will likely corrupt your postgres database the > first time you lose power. (on all the drives I've tested) > > - WB is the only safe option unless you have done lots of plug pull > tests on a drive that is guaranteed to protect data "in flight" during > power loss (Intel disks + maybe the new samsung pcie). I think you have WT (write-through) and WB (write-back) reversed above. -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
