From: Gregory Stark <stark@enterprisedb.com>
To: "Hannes Dorbath" <light@theendofthetunnel.de>
Cc: "Joseph" <spmok2@canada.com>,  <pgsql-performance@postgresql.org>
Subject: Re: FORGOT TO CONFIGURE RAID!       DELL POWEREDGE 2950
In-Reply-To: <46988951.9050108@theendofthetunnel.de> (Hannes Dorbath's message
	of "Sat, 14 Jul 2007 10:29:05 +0200")
Organization: EnterpriseDB
References: <1184357777.135345.38110@n60g2000hse.googlegroups.com>
	<46988951.9050108@theendofthetunnel.de>
Date: Sat, 14 Jul 2007 10:57:55 +0100
Message-ID: <87tzs7b93w.fsf@oxford.xeocode.com>
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"Hannes Dorbath" <light@theendofthetunnel.de> writes:

> From the DELL site it seems this `PERC 5/i' on board controller
> (assuming that's what you have) doesn't even have a BBU. If you don't
> plan to post here in a few weeks again about data corruption, go out and
> shop a serious controller.

This is a bit of a strange comment. A BBU will improve performance but
Postgres doesn't require one to guarantee data integrity.

If your drives have write caching disabled (ie write-through) and your
controller does write-through caching and you leave fsync=on and
full_page_writes=on which is the default then you shouldn't have any data
integrity issues.

Note that many drives, especially IDE drives ship with write caching enabled
(ie, write-back).

And without a BBU many people are tempted to set fsync=off which improves
performance at the cost of data loss on a system crash or power failure. With
a BBU there's no advantage to fsync=off so that temptation to risk data loss
is removed.

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com