From owner-freebsd-current@FreeBSD.ORG  Thu Feb 19 02:56:57 2004
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To: Andre Guibert de Bruet <andy@siliconlandmark.com>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Thu, 19 Feb 2004 03:09:31 EST."
             <20040219025604.D76134@alpha.siliconlandmark.com> 
Date: Thu, 19 Feb 2004 11:56:47 +0100
Message-ID: <26055.1077188207@critter.freebsd.dk>
cc: current@freebsd.org
Subject: Re: Review/Test: Pseudo-device unit number management patch 
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In message <20040219025604.D76134@alpha.siliconlandmark.com>, Andre Guibert de 
Bruet writes:

>The likes of ATA disks include serial numbers in words 10-19. These could
>be used to positively identify a drive when its availability has come
>into question.

But how can you tell if the disk has been mounted and modified in
another computer before it came back ?

There are N ways you can add bandaids and heuristics, but you can not
truly solve the problem, unless you constantly keep a very strong
hash of the entire disk contents in RAM, and check it again if it
comes back which is if not practically impossible, then at least
prohibitively expensive for the added benefit.

Our current operating model is both cheap performance wise, and
simple to understand for users:  Do not remove a storage device you
are still using.

I do not think you should expect this to change significantly in
the future.

-- 
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.