Re: PostgreSQL data dir on linux raid software

On 1/16/07, Bruno Wolff III <bruno(at)wolff(dot)to> wrote:
> On Mon, Jan 15, 2007 at 18:24:19 +0100,
> Federico <rotellaro(at)gmail(dot)com> wrote:
> > Hi,
> > after some test i got that my performance problem described in the
> > message http://archives.postgresql.org/pgsql-admin/2007-01/msg00116.php
> > is issued by the linux software raid 1 on my discs (yes the silicon
> > image controller has only fake raid hardware).
> >
> > I found this old message that seems the same problem like mine.
> >
> > http://archives.postgresql.org/pgsql-admin/2003-12/msg00219.php
> >
> > Because the message is quite old I'm wondering if there're some hdparm
> > settings to enable on the disks that compose the array to have better
> > performances in fsync.
> >
> > For now I cannot mount an expensive scsi raid hardware so i need to
> > have raid software.
>
> Are you using Linux's software raid (md devices) or dmraid using the controller
> to do some of the work? If you aren't using the native linux software raid,
> you might want to try it instead. You will need to rebuild the array to do
> this, so this might not be an easy thing to do. The bios will also need to
> support disabling the raid and exposing the individual disks (but that is
> a fairly normal thing for bios's). If linux can see the individual disks,
> then you should be able to use hdparm to tweak their settings.
>

Hi Bruno,
thank you for the answer.
Yesterday I resolved the issue.
The problem cause was the APIC functionality on my motherboard that
messed the flush on the disk.
Disabling the apic in the bios I got a good performance increase.
With ab i made a test with 1000 request on concurrency 400 and got 20
seconds of mean response time without instance tuning.
:D

Best Regards

Federico Campoli