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From: Magnus Hagander <magnus@hagander.net>
To: Ow Mun Heng <Ow.Mun.Heng@wdc.com>
Cc: Tomas Vondra <tv@fuzzy.cz>
Cc: Ketema <ketema@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Hardware for PostgreSQL
Date: Thu, 01 Nov 2007 07:54:50 +0100
Message-ID: <4729783A.2030201@hagander.net> (raw)
In-Reply-To: <1193889182.7999.71.camel@neuromancer.home.net>
References: <1193849108.591961.103570@22g2000hsm.googlegroups.com>
	<4728FAA1.7060905@fuzzy.cz>
	<1193889182.7999.71.camel@neuromancer.home.net>

Ow Mun Heng wrote:
> On Wed, 2007-10-31 at 22:58 +0100, Tomas Vondra wrote:
> 
>> 2) separate the transaction log from the database
>>
>>     It's mostly written, and it's the most valuable data you have. And in
>>     case you use PITR, this is the only thing that really needs to be
>>     backed up.
> 
> My main DB datastore is in a raid1 array and the xlog is still
> maintained in a single OS drive. Is this considered OK?

Is your OS not RAIDed? I'd keep everything RAIDed one way or another -
otherwise you are certain to get downtime if the disk fails.

Also, if you don't have a *dedicated* disk for the xlog (putting it on
the OS disk doesn't make it dedicated), you miss out on most of the
performance advantage of doing it. The advantage is in that the writes
will be sequential so the disks don't have to seek, but if you have
other access on the same disk, that's not true anymore.

You're likely better off (performance-wise) putting it on the same disk
as the database itself if that one has better RAID, for example.

//Magnus

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