From: Greg Smith <greg@2ndquadrant.com>
To: Scott Carey <scott@richrelevance.com>
Cc: Ireneusz Pluta <ipluta@wp.pl>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: 3ware vs. MegaRAID
Date: Thu, 08 Apr 2010 02:13:32 -0400
Message-ID: <4BBD740C.7020308@2ndquadrant.com> (raw)
In-Reply-To: <23D26E38-9852-4EB6-9DF9-FCB2EAE1EE6C@richrelevance.com>
References: <4BB1FAAF.7050406@wp.pl>
<4BB23254.2040109@2ndquadrant.com>
<4BBB662C.8030102@wp.pl>
<23D26E38-9852-4EB6-9DF9-FCB2EAE1EE6C@richrelevance.com>
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
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Cc: greg@2ndquadrant.com, scott@richrelevance.com, ipluta@wp.pl
Subject: Re: 3ware vs. MegaRAID
In-Reply-To: <4BBD740C.7020308@2ndquadrant.com>
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