Re: [Testperf-general] dbt2 & opteron performance

On Fri, 29 Jul 2005 14:39:08 -0500
"Jim C. Nasby" <decibel@decibel.org> wrote:

> 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@osdl.org> wrote:
> > 
> > > On Thu, 28 Jul 2005 18:48:09 -0500
> > > "Jim C. Nasby" <decibel@decibel.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@decibel.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.

I have done that before actually, when the tablespace patch came out.  I
was able to get almost 40% more throughput with half the drives than
striping all the disks together.

Mark