Re: RAID + PostgreSQL?

Compaq RAID controllers are known to be slow under linux.

Alex.

On 6/26/06, Tony Caduto <tony_caduto(at)amsoftwaredesign(dot)com> wrote:
>
> Scott Marlowe wrote:
> > On Mon, 2006-06-26 at 08:59, Tony Caduto wrote:
> >
> >> MG wrote:
> >>
> >>> Hello,
> >>>
> >>> we are using PostgreSQL 8.0.3 together with RAID on OpenServer 6.
> >>>
> >>> When we do a big SELECT-query the whole maschine becomes very very
> >>> very slowly or stands.
> >>> The maschine has 3 GB RAM, so we suppose it`s the RAID.
> >>>
> >>> Has anyone some experience with RAID + PostgreSQL?
> >>>
> >>> Where does PostgreSQL saves his temporary files? Perhaps these are the
> >>> reason for the bad performance.
> >>>
> >>> Greetings
> >>>
> >>> Michaela
> >>>
> >> What kind of RAID? I know if you have it set up to mirror it becomes
> >> slow as pond water.
> >>
> >
> > I have to say this has NOT been my experience. With a pair of U320
> > drives on an LSI-Megaraid with battery backed cache (256M or 512M, not
> > sure which it was, it's been a few years) our pg server was noticeable
> > faster with a mirror set than with a single IDE drive (with cache
> > disabled) on the same machine. And faster than a single SCSI drive with
> > no RAID controller as well.
> >
> >
> Hi Scott,
>
> We are just using the compaq hardware SCSI //raid included with the
> server and it does not have a
> battery backed cache. Actually my test DB running the same queries on a
> cheap IDE drive (on a Athlon 2200+ where 50% faster than the compaq
> running the mirrored
> SCSI drives. The compaq system was also a Dual 2.4 gzh Xeon with 2.5 GB
> of memory and the Athlon had 512mb. Some of the performance on the
> Athlon could be attributed to the CPU, but mostly the IDE drive just
> blew away the mirrored SCSI drive
> On the Compaq system setting Fsync to false increased the speed of all
> select statements, not just complex ones with sorting.
>
> I didn't set up the hardware, so I don't know if the system admin guy
> screwed anything up in the raid setup.
>
> Later,
>
> --
> Tony Caduto
> AM Software Design
> http://www.amsoftwaredesign.com
> Home of PG Lightning Admin for Postgresql
> Your best bet for Postgresql Administration
>
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