From: Dimitri Fontaine <dfontaine@hi-media.com>
To: pgsql-performance@postgresql.org
Subject: Re: dell versus hp
Date: Thu, 8 Nov 2007 21:14:36 +0100
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Cc: "Scott Marlowe" <scott.marlowe@gmail.com>,
	"Vivek Khera" <khera@kcilink.com>
References: <82607932-FC46-4B73-BF78-2290EE55F7F5@pvv.ntnu.no>
	<44B74F2E-29A6-4746-B8A8-E9355CC2F527@kcilink.com>
	<dcc563d10711081022i9a8a64fg2fe00e6159027426@mail.gmail.com>
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Le Thursday 08 November 2007 19:22:48 Scott Marlowe, vous avez =E9crit=A0:
> On Nov 8, 2007 10:43 AM, Vivek Khera <khera@kcilink.com> wrote:
> > On Nov 6, 2007, at 1:10 PM, Greg Smith wrote:
> > > elsewhere.  But once you have enough disks in an array to spread all
> > > the load over that itself may improve write throughput enough to
> > > still be a net improvement.
> >
> > This has been my expeience with 14+ disks in an array (both RAID10 and
> > RAID5).  The difference is barely noticeable.
>
> Mine too.

May we conclude from this that mixing WAL and data onto the same array is a=
=20
good idea starting at 14 spindles?

The Dell 2900 5U machine has 10 spindles max, that would make 2 for the OS=
=20
(raid1) and 8 for mixing WAL and data... not enough to benefit from the mov=
e,=20
or still to test?

> I would suggest though, that by the time you get to 14=20
> disks, you switch from RAID-5 to RAID-6 so you have double redundancy.
>  Performance of a degraded array is better in RAID6 than RAID5, and
> you can run your rebuilds much slower since you're still redundant.

Is raid6 better than raid10 in term of overall performances, or a better cu=
t=20
when you need capacity more than throughput?

Thanks for sharing the knowlegde, regards,
=2D-=20
dim