Re: Review/Test: Pseudo-device unit number management patch

From: Poul-Henning Kamp (phk_at_phk.freebsd.dk)
Date: 02/19/04

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    To: Andre Guibert de Bruet <andy@siliconlandmark.com>
Date: Thu, 19 Feb 2004 11:56:47 +0100

    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.
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