From owner-freebsd-arch@FreeBSD.ORG  Thu Jun  9 19:42:24 2005
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To: Pawel Jakub Dawidek <pjd@FreeBSD.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Thu, 09 Jun 2005 21:30:08 +0200."
	<20050609193008.GB837@darkness.comp.waw.pl> 
Date: Thu, 09 Jun 2005 21:42:15 +0200
Message-ID: <9131.1118346135@critter.freebsd.dk>
Sender: phk@critter.freebsd.dk
Cc: arch@FreeBSD.org
Subject: Re: simplify disksort, please review. 
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In message <20050609193008.GB837@darkness.comp.waw.pl>, Pawel Jakub Dawidek writes:

>The one example of how the order can be broken (write(offset, size)):
>
>	write(1024, 512)
>	write(0, 2048)

If you issue these two requests just like that, you get no guarantee
which order they get written in.

It's not just disksort which might surprise you, tagged queuing and
write caches may mess up your day as well.

-- 
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.