From: Scott Marlowe <scott.marlowe@gmail.com>
To: Craig James <craig_james@emolecules.com>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: How to allocate 8 disks
Date: Sat, 1 Mar 2008 12:47:56 -0600
Message-ID: <dcc563d10803011047h533a7ea6xb3a4ecb00b45ec05@mail.gmail.com> (raw)
In-Reply-To: <47C99B3E.4010606@emolecules.com>
References: <1204285894.11773.33.camel@franck-gusty>
<dcc563d10802290613v482f52dr43ea95b52886de31@mail.gmail.com>
<1204296705.11773.51.camel@franck-gusty>
<Pine.GSO.4.64.0802291019570.28452@westnet.com>
<47C88826.4040209@paradise.net.nz>
<47C99B3E.4010606@emolecules.com>
On Sat, Mar 1, 2008 at 12:06 PM, Craig James <craig_james@emolecules.com> wrote:
> We're upgrading to a medium-sized server, a Dell PowerEdge 2950, dual-quad CPU's and 8 GB memory. This box can hold at most 8 disks (10K SCSI 2.5" 146 GB drives) and has Dell's Perc 6/i RAID controller.
>
> I'm thinking of this:
>
> 6 disks RAID 1+0 Postgres data
> 1 disk WAL
> 1 disk Linux
>
> I've often seen RAID 1 recommended for the WAL. Is that strictly for reliability, or is there a performance advantage to RAID 1 for the WAL?
>
> It seems to me separating the OS and WAL on two disks is better than making a single RAID 1 and sharing it, from a performance point of view.
It's a trade off. Remember that if the single disk hold xlog fails
you've just quite possubly lost your database. I'd be inclined to
either using a RAID-1 of two disks for the OS and xlog, and having
pgsql log to the 6 disk RAID-10 instead of the OS / xlog disk set.
More important, do you have battery backed cache on the controller? A
good controller with a battery backed cache can usually outrun a
larger array with no write cache when it comes to transactions /
writing to the disks.
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To: pgsql-performance@postgresql.org
Cc: scott.marlowe@gmail.com, craig_james@emolecules.com
Subject: Re: How to allocate 8 disks
In-Reply-To: <dcc563d10803011047h533a7ea6xb3a4ecb00b45ec05@mail.gmail.com>
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