On Fri, 2009-03-13 at 11:41 -0700, Ben Chobot wrote: > On Fri, 13 Mar 2009, Joshua D. Drake wrote: > > >> It seems to me that all you get with a BBU-enabled card is the ability to > >> get burts of writes out of the OS faster. So you still have the problem, > >> it's just less like to be encountered. > > > > A BBU controller is about more than that. It is also supposed to be > > about data integrity. The ability to have unexpected outages and have > > the drives stay consistent because the controller remembers the state > > (if that is a reasonable way to put it). > > Of course. But if you can't reliably flush the OS buffers (because, say, > you're using LVM so fsync() doesn't work), then you can't say what > actually has made it to the safety of the raid card.
Wait, actually a good BBU RAID controller will disable the cache on the drives. So everything that is cached is already on the controller vs. the drives itself. Or am I missing something? Joshua D. Drake > -- PostgreSQL - XMPP: jdr...@jabber.postgresql.org Consulting, Development, Support, Training 503-667-4564 - http://www.commandprompt.com/ The PostgreSQL Company, serving since 1997 -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
