Matthew Wakeling <matthew@xxxxxxxxxxx> wrote: > On Thu, 3 Jun 2010, Craig James wrote: >>> Also, are barriers *on* on the RAID1 mount and off on the RAID10 one? >> >> It was the barriers. "barrier=1" isn't just a bad idea on ext4, >> it's a disaster. > > This worries me a little. Does your array have a battery-backed > cache? If so, then it should be fast regardless of barriers > (although barriers may make a small difference). If it does not, > then it is likely that the fast speed you are seeing with barriers > off is unsafe. I've seen this, too (with xfs). Our RAID controller, in spite of having BBU cache configured for writeback, waits for actual persistence on disk for write barriers (unlike for fsync). This does strike me as surprising to the point of bordering on qualifying as a bug. It means that you can't take advantage of the BBU cache and get the benefit of write barriers in OS cache behavior. :-( -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
