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Re: Opinions on Raid

From: Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>
To: Joe Uhl <joeuhl(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Opinions on Raid
Date: 2007-02-27 13:56:08
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Lists: pgsql-performance
Joe Uhl wrote:
> We have been running Postgres on a 2U server with 2 disks configured in
> raid 1 for the os and logs and 4 disks configured in raid 10 for the
> data.  I have since been told raid 5 would have been a better option
> given our usage of Dell equipment and the way they handle raid 10.  I
> have just a few general questions about raid with respect to Postgres:
> [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.

this depends a lot on the raidcontroller (whether it has or not BBWC for 
example) - for some use-cases softwareraid is actually faster(especially 
for seq-io tests).

> [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.

well the answer to that question depends on what you are using for your 
network monitoring as a whole as well as your Platform of choice. If you 
use say nagios and Linux it makes sense to use a nagios plugin (we do 
that here with a unified check script that checks everything from 
LSI-MPT based raid cards, over IBMs ServeRAID, HPs Smartarray,LSI 
MegaRAID cards and also Linux/Solaris Software RAID).
If you are using another monitoring solution(OpenView, IBM 
Directory,...) your solution might look different.


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