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Re: Performance Characteristics of All Linux RAIDs (mdadm/bonnie++)

To: Bill Davidsen <davidsen@xxxxxxx>
Subject: Re: Performance Characteristics of All Linux RAIDs (mdadm/bonnie++)
From: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
Date: Thu, 29 May 2008 12:22:23 +0100
Cc: Jens BÃckman <jens.backman@xxxxxxxxx>, Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <483DE40D.8090608@tmr.com>
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References: <alpine.DEB.1.10.0805280442330.4527@p34.internal.lan> <95711f160805280934y77ed7d91tec5aeb531bf8013c@mail.gmail.com> <20080528195752.0cdcbc6d@core> <483DE40D.8090608@tmr.com>
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> I really don't think that's any part of the issue, the same memory and 
> bridge went 4-5x faster in other read cases. The truth is that the 
> raid-1 performance is really bad, and it's the code causing it AFAIK. If 
> you track the actual io it seems to read one drive at a time, in order, 
> without overlap.

Make sure the readahead is set to be a fair bit over the stripe size if
you are doing bulk data tests for a single file. (Or indeed in the real
world for that specific case ;))

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