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Date: Mon, 16 Jul 2001 02:50:02 +1200
From: Chris Wedgwood <cw@f00f.org>
To: Ken Hirsch <kenhirsch@myself.com>
Cc: John Alvord <jalvo@mbay.net>, Daniel Phillips <phillips@bonn-fries.net>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
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        mike@bigstorage.com, kevin@bigstorage.com, linux-lvm@sistina.com
Subject: Re: [PATCH] 64 bit scsi read/write
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On Sun, Jul 15, 2001 at 09:16:09AM -0400, Ken Hirsch wrote:

    The first technique is not sufficient with modern disk
    controllers, which may reorder sector writes within a block.  A
    checksum, especially a robust CRC32, is sufficient, but rather
    expensive.

So you write the number to the start and end of each sector, or, you
only assume sector-wide 'block-sizes' for integrity.

A 32-bit CRC is plenty cheap enough on modern CPUs and especially
considering how often you need to calculate it.

    Mohan has a clever technique that is computationally trivial and
    only uses one bit per sector:
    http://www.almaden.ibm.com/u/mohan/ICDE95.pdf
    
    Unfortunately, it's also patented:
    http://www.delphion.com/details?pn=US05418940__
    
    Perhaps IBM will clarify their position with respect to free
    software and patents in the upcoming conference.

Wow... pretty neat, but fortunately not necessary.



  --cw
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