Message-ID: <4BBD740C.7020308@2ndquadrant.com>
Date: Thu, 08 Apr 2010 02:13:32 -0400
From: Greg Smith <greg@2ndquadrant.com>
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To: Scott Carey <scott@richrelevance.com>
CC: Ireneusz Pluta <ipluta@wp.pl>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: 3ware vs. MegaRAID
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	<23D26E38-9852-4EB6-9DF9-FCB2EAE1EE6C@richrelevance.com>
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Scott Carey wrote:
> * Change the linux 'readahead' block device parameter to at least 4MB (8192, see blockdev --setra) -- I don't know if there is a FreeBSD equivalent.
>   
I haven't tested them, but 3ware gives suggestions at 
http://www.3ware.com/kb/Article.aspx?id=14852 for tuning their cards 
properly under FreeBSD.  You cannot get good sequential read performance 
from 3ware's cards without doing something about this at the OS level; 
the read-ahead on the card itself is minimal and certainly a bottleneck.

As for your comments about drives being faster at the front than the 
end, the zcav tool that comes with bonnie++ is a good way to plot that 
out, rather than having to split partitions up and do a bunch of manual 
testing.

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