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To: Alexander Motin <mav@FreeBSD.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Fri, 25 Dec 2009 16:03:05 +0200."
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Date: Fri, 25 Dec 2009 18:19:01 +0000
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Cc: FreeBSD-Current <freebsd-current@FreeBSD.org>, freebsd-arch@FreeBSD.org
Subject: Re: File system blocks alignment 
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In message <4B34C619.7070505@FreeBSD.org>, Alexander Motin writes:
>Poul-Henning Kamp wrote:

>- Second is a row size - stripe size * number of data disks. You may
>freely read less information then full row, but short write cause RAID
>to handle read-modify-write scenario.

There is a far worse scenario: a stripe-spanning write, it forces a
RMW cycle over two different RAID5 stripes.

-- 
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.