From: Alan Hodgson <ahodgson@simkin.ca>
Organization: Simkin Network Consulting
To: pgsql-performance@postgresql.org
Subject: Re: Advice configuring ServeRAID 8k for performance
Date: Thu, 5 Aug 2010 16:58:13 -0700
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	<4C5B4A0C.5080508@catalyst.net.nz>
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On Thursday, August 05, 2010, Mark Kirkwood <mark.kirkwood@catalyst.net.nz> 
wrote:
> Normally I'd agree with the others and recommend RAID10 - but you say
> you have an OLAP workload - if it is *heavily* read biased you may get
> better performance with RAID5 (more effective disks to read from).
> Having said that, your sequential read performance right now is pretty
> low (151 MB/s  - should be double this), which may point to an issue
> with this controller. Unfortunately this *may* be important for an OLAP
> workload (seq scans of big tables).

Probably a low (default) readahead limitation. ext3 doesn't help but it can 
usually get up over 400MB/sec. Doubt it's the controller.

-- 
"No animals were harmed in the recording of this episode. We tried but that 
damn monkey was just too fast."