Re: Raid 10 chunksize

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