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From: Greg Smith <greg@2ndquadrant.com>
To: Ryan Wexler <ryan@iridiumsuite.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: performance on new linux box
Date: Mon, 12 Jul 2010 11:23:16 -0400
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Ryan Wexler wrote:
> One question I do have is this card has a setting called Read Policy 
> which apparently helps with sequentially reads.  Do you think that is 
> something I should enable?

Linux will do some amount of read-ahead in a similar way on its own.  
You run "blockdev --getra" and "blockdev --setra" on each disk device on 
the system to see the settings and increase them.  I've found that 
tweaking there, where you can control exactly the amount of readahead, 
to be more effective than relying on the less tunable Read Policy modes 
in RAID cards that do something similar.  That said, it doesn't seem to 
hurt to use both on the LSI card you have; giving more information there 
to the controller for its use in optimizing how it caches things, by 
changing to the more aggressive Read Policy setting, hasn't ever 
degraded results significantly when I've tried.

-- 
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com   www.2ndQuadrant.us




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