From owner-freebsd-performance@FreeBSD.ORG  Mon May  2 13:15:10 2005
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To: Eric Anderson <anderson@centtech.com>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Mon, 02 May 2005 08:10:52 CDT."
             <427626DC.5030702@centtech.com> 
Date: Mon, 02 May 2005 15:15:06 +0200
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cc: Robert Watson <rwatson@freebsd.org>
cc: =?ISO-8859-15?Q?=22Arne_=5C=22W=F6rner=5C=22=22?= <arne_woerner@yahoo.com>
Subject: Re: Very low disk performance on 5.x 
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In message <427626DC.5030702@centtech.com>, Eric Anderson writes:

>Don't mean to be terse here, but I'm talking about the same test done an 
>two different RAID5 configurations, with different disks, and not just 
>me - other users in this very thread see the same issue..

Uhm, if you are using RAID5 and your requests are not aligned and
sized after the RAID5 you should *expect* read performance to be poor.

If you your request ends up accessing two different blocks even just
once per stripe, this totally kills performance.


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.