From: Greg Smith <gsmith@gregsmith.com>
To: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: 12 disks raid setup
Date: Fri, 29 Feb 2008 23:56:54 -0500 (EST)
Message-ID: <Pine.GSO.4.64.0802292347250.145@westnet.com> (raw)
In-Reply-To: <47C8A6D9.1050502@Sheeky.Biz>
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>
<47C8A6D9.1050502@Sheeky.Biz>
On Sat, 1 Mar 2008, Shane Ambler wrote:
> It may be the way you have worded this but it makes it sound like the
> cache and the battery backup are as one (or that the cache doesn't work
> unless you have the battery)...If the raid card has the cache without
> the battery you would get the performance figures you mentioned, you
> just wouldn't have the reliability of finishing writes after a power off
> situation.
Wording is intentional--if you don't have a battery for it, the cache has
to be turned off (or set to write-through so it's only being used on
reads) in order for the database to be reliable. If you can't finish
writes after a power off, you can't cache writes and expect your database
to survive for too long.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
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To: pgsql-performance@postgresql.org
Cc: gsmith@gregsmith.com
Subject: Re: 12 disks raid setup
In-Reply-To: <Pine.GSO.4.64.0802292347250.145@westnet.com>
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