>>> On Thu, Nov 8, 2007 at 2:14 PM, in message
<200711082114.36788.dfontaine@hi-media.com>, Dimitri Fontaine
<dfontaine@hi-media.com> wrote:
> The Dell 2900 5U machine has 10 spindles max, that would make 2 for the OS
> (raid1) and 8 for mixing WAL and data... not enough to benefit from the
> move,
> or still to test?
From our testing and various posts on the performance list, you can
expect a good battery backed caching RAID controller will probably
eliminate most of the performance difference between separate WAL
drives and leaving them on the same RAID array with the rest of the
database. See, for example:
http://archives.postgresql.org/pgsql-performance/2007-02/msg00026.php
Ben found a difference of "a few percent"; I remember seeing a post
from someone who did a lot of testing and found a difference of 1%.
As stated in the above referenced posting, it will depend on your
workload (and your hardware) so it is best if you can do some
realistic tests.
-Kevin