From: Geoff Tolley <geoff@polimetrix.com>
To: Joe Uhl <joeuhl@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Opinions on Raid
Date: Tue, 27 Feb 2007 15:42:36 -0800
Message-ID: <45E4C1EC.2070807@polimetrix.com> (raw)
In-Reply-To: <1172581920.28858.1176750095@webmail.messagingengine.com>
References: <1172581920.28858.1176750095@webmail.messagingengine.com>
Joe Uhl wrote:
> [1] What is the performance penalty of software raid over hardware raid?
> Is it truly significant? We will be working with 100s of GB to 1-2 TB
> of data eventually.
One thing you should appreciate about hw vs sw raid is that with the former
you can battery-back it and enable controller write caching in order to
make disk write latency largely disappear. How much of a performance
difference that makes depends on what you're doing with it, of course.
See the current thread "Two hard drives --- what to do with them?" for some
discussion of the virtues of battery-backed raid.
> [2] How do people on this list monitor their hardware raid? Thus far we
> have used Dell and the only way to easily monitor disk status is to use
> their openmanage application. Do other controllers offer easier means
> of monitoring individual disks in a raid configuration? It seems one
> advantage software raid has is the ease of monitoring.
Personally I use nagios with nrpe for most of the monitoring, and write a
little wrapper around the cli monitoring tool from the controller
manufacturer to grok whether it's in a good/degraded/bad state.
Dell PERC controllers I think are mostly just derivatives of Adaptec/LSI
controllers, so you might be able to get a more convenient monitoring tool
from one of them that might work. See if you can find your PERC version in
http://pciids.sourceforge.net/pci.ids, or if you're using Linux then which
hw raid module is loaded for it, to get an idea of which place to start
looking for that.
- Geoff
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To: pgsql-performance@postgresql.org
Cc: geoff@polimetrix.com, joeuhl@gmail.com
Subject: Re: Opinions on Raid
In-Reply-To: <45E4C1EC.2070807@polimetrix.com>
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