Re: two disks - best way to use them?

On Tue, 6 Dec 2005, Thomas Harold wrote:

> Ron wrote:
>
>> For accuracy's sake, which exact config did you finally use?
>>
>> How did you choose the config you finally used? Did you test the three
>> options or just pick one?
>
> (Note: I'm not the original poster.)
>
> I just picked the option of putting the data/pg_xlog directory (WAL) on a 2nd
> set of spindles. That was the easiest thing for me to change on this test
> box.
>
> The test server is simply a Gentoo box running software RAID and LVM2. The
> primary disk set is 2x7200RPM 300GB drives and the secondary disk set is
> 2x5400RPM 300GB drives. Brand new install of PGSQL 8.1, with mostly default
> settings (I changed FSM pages to be a higher value, max_fsm_pages = 150000).
> PGSQL was given it's own ext3 32GB LVM volume on the primary disk set
> (2x7200RPM). Originally, all files were on the primary disk.

the WAL is more sensitive to drive speeds then the data is, so you may
pick up a little more performance by switching the WAL to the 7200 rpm
drives instead of the 5400 rpm drives.

if you see a noticable difference with this, consider buying a pair of
smaller, but faster drives (10k or 15k rpm drives, or a solid-state
drive). you can test this (with significant data risk) by putting the WAL
on a ramdisk and see what your performance looks like.

David Lang