On Fri, 2006-02-10 at 16:39, Ragnar wrote:
> On Fri, 2006-02-10 at 11:24 +0100, Markus Schaber wrote:
>
> > For lots non-read-only database workloads, RAID5 is a performance
> > killer. Raid 1/0 might be better, or having two mirrors of two disks
> > each, the first mirror holding system, swap, and the PostgreSQL WAL
> > files, the second one holding the data.
>
> I was under the impression that it is preferable to keep the WAL on
> its own spindles with no other activity there, to take full advantage
> of the sequential nature of the WAL writes.
>
> That would mean one mirror for the WAL, and one for the rest.
> This, of course, may sometimes be too much wasted disk space, as the WAL
> typically will not use a whole disk, so you might partition this mirror
> into a small ext2 filesystem for WAL, and use the rest for files seldom
> accessed, such as backups.
Well, on most database servers, the actual access to the OS and swap
drives should drop to about zero over time, so this is a workable
solution if you've only got enough drives / drive slots for two mirrors.