Re: Filesystem setup on new system

On Thu, 7 Aug 2008, Henrik wrote:

> My first idea was to have one partition on the RAID 10 using ext3 with
> data=writeback, noatime as mount options.
>
> But I wonder if I should have 2 partitions on the RAID 10 one for the PGDATA
> dir using ext3 and one partition for XLOGS using ext2.

Really depends on your write volume.  The write cache on your controller
will keep having a separate xlog disk from being as important as it is
without one.  If your write volume is really high though, it may still be
a bottleneck, and you may discover your app runs better with a dedicated
ext2 xlog disk instead.

The simple version is:

WAL write volume extremely high->dedicated xlog can be better

WAL volume low->more disks for the database array better even if that
mixes the WAL on there as well

If you want a true answer for which is better, you have to measure your
application running on this hardware.

> 6 SAS 15K drives in RAID 10 on one of the SAN controllers for database

With only 6 disks available, in general you won't be able to reach the WAL
as a bottleneck before being limited by seeks on the remaining 4 database
disks, so you might as well group all 6 together.  It's possible your
particular application might prefer it the other way though, if you're
doing a while lot of small writes for example.  I've seen a separate WAL
handle low-level benchmarks better, but on more real-world loads it's
harder to run into that situation.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD