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

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Date:	Thu, 29 May 2008 12:22:23 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Bill Davidsen <davidsen@....com>
Cc:	Jens Bäckman <jens.backman@...il.com>,
	Justin Piszcz <jpiszcz@...idpixels.com>,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	xfs@....sgi.com
Subject: Re: Performance Characteristics of All Linux RAIDs (mdadm/bonnie++)

> 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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