Scott Carey wrote:
A little extra info here >> md, LVM, and some other tools do not allow the file system to use write barriers properly.... So those are on the bad list for data integrity with SAS or SATA write caches without battery back-up. However, this is NOT an issue on the postgres data partition. Data fsync still works fine, its the file system journal that might have out-of-order writes. For xlogs, write barriers are not important, only fsync() not lying. As an additional note, ext4 uses checksums per block in the journal, so it is resistant to out of order writes causing trouble. The test compared to here was on ext4, and most likely the speed increase is partly due to that.
[Looks at Stef's config - 2x 7200 rpm SATA RAID 0] I'm still highly suspicious of such a system being capable of outperforming one with the same number of (effective) - much faster - disks *plus* a dedicated WAL disk pair... unless it is being a little loose about fsync! I'm happy to believe ext4 is better than ext3 - but not that much!
However, its great to have so many different results to compare against! Cheers Mark -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
