Dan Langille wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Bruce Momjian wrote: > > Matthew Wakeling wrote: > >> On Fri, 13 Nov 2009, Greg Smith wrote: > >>> In order for a drive to work reliably for database use such as for > >>> PostgreSQL, it cannot have a volatile write cache. You either need a write > >>> cache with a battery backup (and a UPS doesn't count), or to turn the cache > >>> off. The SSD performance figures you've been looking at are with the drive's > >>> write cache turned on, which means they're completely fictitious and > >>> exaggerated upwards for your purposes. In the real world, that will result > >>> in database corruption after a crash one day. > >> Seagate are claiming to be on the ball with this one. > >> > >> http://www.theregister.co.uk/2009/12/08/seagate_pulsar_ssd/ > > > > I have updated our documentation to mention that even SSD drives often > > have volatile write-back caches. Patch attached and applied. > > Hmmm. That got me thinking: consider ZFS and HDD with volatile cache. > Do the characteristics of ZFS avoid this issue entirely? No, I don't think so. ZFS only avoids partial page writes. ZFS still assumes something sent to the drive is permanent or it would have no way to operate. -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com PG East: http://www.enterprisedb.com/community/nav-pg-east-2010.do + If your life is a hard drive, Christ can be your backup. + -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
