Re: Article about PostgreSQL and RAID in Brazil

On Thu, Sep 16, 2004 at 02:07:37PM -0700, Josh Berkus wrote:
> Jim,
>
> > What about benefits from putting WAL and pg_temp on seperate drives?
> > Specifically, we have a box with 8 drives, 2 in a mirror with the OS and
> > WAL and pg_temp; the rest in a raid10 with the database on it. Do you
> > think it would have been better to make one big raid10? What if it was
> > raid5? And what if it was only 6 drives total?
>
> OSDL's finding was that even with a large RAID array, it still benefits you to
> have WAL on a seperate disk resource ... substantially, like 10% total
> performance.    However, your setup doesn't get the full possible benefit,
> since WAL is sharing the array with other resources.

Yes, but if a 3 drive raid array is 40% slower than a single disk it
seems like the 10% benefit for having WAL on a seperate drive would
still be a losing proposition.

BTW, my experience with our setup is that the raid10 is almost always
the IO bottleneck, and not the mirror with everything else on it.
--
Jim C. Nasby, Database Consultant               decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828

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