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Re: [Testperf-general] dbt2 & opteron performance

From: "Jim C(dot) Nasby" <decibel(at)decibel(dot)org>
To: Mark Wong <markw(at)osdl(dot)org>
Cc: testperf-general(at)pgfoundry(dot)org, pgsql-hackers(at)postgresql(dot)org
Subject: Re: [Testperf-general] dbt2 & opteron performance
Date: 2005-07-29 19:39:08
Message-ID: 20050729193908.GA95931@decibel.org (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, Jul 28, 2005 at 05:00:44PM -0700, Mark Wong wrote:
> On Thu, 28 Jul 2005 16:55:55 -0700
> Mark Wong <markw(at)osdl(dot)org> wrote:
> 
> > On Thu, 28 Jul 2005 18:48:09 -0500
> > "Jim C. Nasby" <decibel(at)decibel(dot)org> wrote:
> > 
> > > On Thu, Jul 28, 2005 at 04:15:31PM -0700, Mark Wong wrote:
> > > > On Thu, 28 Jul 2005 17:17:25 -0500
> > > > "Jim C. Nasby" <decibel(at)decibel(dot)org> wrote:
> > > > 
> > > > > On Wed, Jul 27, 2005 at 07:32:34PM -0700, Josh Berkus wrote:
> > > > > > > This 4-way has 8GB of memory and four Adaptec 2200s controllers attached
> > > > > > > to 80 spindles (eight 10-disk arrays).  For those familiar with the
> > > > > > > schema, here is a visual of the disk layout:
> > > > > > > 	http://www.osdl.org/projects/dbt2dev/results/dev4-015/layout-6.html
> > > > > 
> > > > > Have you by-chance tried it with the logs and data just going to
> > > > > seperate RAID10s? I'm wondering if a large RAID10 would do a better job
> > > > > of spreading the load than segmenting things to specific drives.
> > > > 
> > > > No, haven't tried that.  That would reduce my number of spindles as I
> > > > scale up. ;)  I have the disks attached as JBODs and use LVM2 to stripe
> > > > the disks together.
> > > 
> > > I'm confused... why would it reduce the number of spindles? Is
> > > everything just striped right now? You could always s/RAID10/RAID0/.
> > 
> > RAID10 requires a minimum of 4 devices per LUN, I think.  At least 2
> > devices in a mirror, at least 2 mirrored devices to stripe.
> > 
> > RAID0 wouldn't be any different than what I have now, except if I use
> > hardware RAID I can't stripe across controllers.  That's treating LVM2
> > striping equal to software RAID0 of course.
> 
> Oops, spindles was the wrong word to describe what I was losing.  But I
> wouldn't be able to spread the reads/writes across as many spindles if I
> have any mirroring.

Not sure I fully understand what you're trying to say, but it seems like
it might still be worth trying my original idea of just turning all 80
disks into one giant RAID0/striped array and see how much more bandwidth
you get out of that. At a minimum it would allow you to utilize the
remaining spindles, which appear to be unused right now.
-- 
Jim C. Nasby, Database Consultant               decibel(at)decibel(dot)org 
Give your computer some brain candy! www.distributed.net Team #1828

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