On Wed, Aug 09, 2006 at 10:15:27AM -0500, Scott Marlowe wrote:
> Actually, the BIGGEST win comes when you've got battery backed cache on
> your RAID controller. In fact, I'd spend money on a separate RAID
> controller for xlog with its own cache hitting a simple mirror set
> before I'd spring for more drives on pg_xlog. The battery backed cache
> on the pg_xlog likely wouldn't need to be big, just there and set to
> write-back.
>
> Then put all the rest of your cash into disks on a big RAID 10 config,
> and as big of a battery backed cache as you can afford for it and memory
> for the machine.
Actually, my (limited) testing has show than on a good battery-backed
controller, there's no penalty to leaving pg_xlog in with the rest of
PGDATA. This means that the OP could pile all 8 drives into a RAID10,
which would almost certainly do better than 6+2.
Note that some controllers (such as 3ware) need to periodically test the
life of the BBU, and they disable write caching when they do so, which
would tank performance.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461