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Date: Thu, 11 Sep 2008 12:23:32 -0500
From: Kenneth Marshall <ktm@rice.edu>
To: Matthew Wakeling <matthew@flymine.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: Choosing a filesystem
Message-ID: <20080911172332.GP6714@it.is.rice.edu>
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	<alpine.DEB.1.10.0809111814130.4454@aragorn.flymine.org>
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On Thu, Sep 11, 2008 at 06:18:37PM +0100, Matthew Wakeling wrote:
> On Thu, 11 Sep 2008, Laszlo Nagy wrote:
>> So the basic system will reside on a RAID 1 array, created from two SAS 
>> disks spinning at 15 000 rpm. I will buy 10 pieces of Seagate Barracuda 
>> 320GB SATA (ES 7200) disks for the rest.
>
> That sounds good. Put RAID 1 on the pair, and RAID 1+0 on the rest. It'll 
> be pretty good. Put the OS and the WAL on the pair, and the database on the 
> large array.
>
> However, one of the biggest things that will improve your performance 
> (especially in OLTP) is to use a proper RAID controller with a 
> battery-backed-up cache.
>
> Matthew
>

But remember that putting the WAL on a separate drive(set) will only
help if you do not have competing I/O, such as system logging or paging,
going to the same drives. This turns your fast sequential I/O into
random I/O with the accompaning 10x or more performance decrease.

Ken