Message-ID: <45E4C1EC.2070807@polimetrix.com>
Date: Tue, 27 Feb 2007 15:42:36 -0800
From: Geoff Tolley <geoff@polimetrix.com>
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To: Joe Uhl <joeuhl@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: Opinions on Raid
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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