From: Jim C. Nasby <jnasby@pervasive.com>
To: Scott Marlowe <smarlowe@g2switchworks.com>
Cc: Thomas F. O'Connell <tfo@sitening.com>
Cc: Joshua D.Drake <jd@commandprompt.com>
Cc: Kenji Morishige <kenjim@juniper.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: most bang for buck with ~ $20,000
Date: Wed, 9 Aug 2006 16:35:43 -0500
Message-ID: <20060809213543.GV40481@pervasive.com> (raw)
In-Reply-To: <1155136527.20252.90.camel@state.g2switchworks.com>
References: <20060808204354.GN29379@juniper.net>
<44D906E1.7010405@commandprompt.com>
<9EE66C7F-0B04-4472-9EBD-CD567AC9EA1D@sitening.com>
<44D90FFE.7010807@commandprompt.com>
<82C06632-148B-4489-90EB-BBB8A6BD1159@sitening.com>
<1155136527.20252.90.camel@state.g2switchworks.com>
On Wed, Aug 09, 2006 at 10:15:27AM -0500, Scott Marlowe wrote:
> Actually, the BIGGEST win comes when you've got battery backed cache on
> your RAID controller. In fact, I'd spend money on a separate RAID
> controller for xlog with its own cache hitting a simple mirror set
> before I'd spring for more drives on pg_xlog. The battery backed cache
> on the pg_xlog likely wouldn't need to be big, just there and set to
> write-back.
>
> Then put all the rest of your cash into disks on a big RAID 10 config,
> and as big of a battery backed cache as you can afford for it and memory
> for the machine.
Actually, my (limited) testing has show than on a good battery-backed
controller, there's no penalty to leaving pg_xlog in with the rest of
PGDATA. This means that the OP could pile all 8 drives into a RAID10,
which would almost certainly do better than 6+2.
Note that some controllers (such as 3ware) need to periodically test the
life of the BBU, and they disable write caching when they do so, which
would tank performance.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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To: pgsql-performance@postgresql.org
Cc: jnasby@pervasive.com, smarlowe@g2switchworks.com, tfo@sitening.com, jd@commandprompt.com, kenjim@juniper.net
Subject: Re: most bang for buck with ~ $20,000
In-Reply-To: <20060809213543.GV40481@pervasive.com>
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