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[linux-lvm] Re: [PATCH] 64 bit scsi read/write
- From: "Ken Hirsch" <kenhirsch myself com>
- To: "Chris Wedgwood" <cw f00f org>,"John Alvord" <jalvo mbay net>
- Cc: "Daniel Phillips" <phillips bonn-fries net>,"Alan Cox" <alan lxorguk ukuu org uk>,"Andrew Morton" <andrewm uow edu au>,"Andreas Dilger" <adilger turbolinux com>,"Albert D. Cahalan" <acahalan cs uml edu>,"Ben LaHaise" <bcrl redhat com>,"Ragnar Kjxrstad" <kernel ragnark vestdata no>,<linux-fsdevel vger kernel org>,<linux-kernel vger kernel org>,<mike bigstorage com>,<kevin bigstorage com>,<linux-lvm sistina com>
- Subject: [linux-lvm] Re: [PATCH] 64 bit scsi read/write
- Date: Sun, 15 Jul 2001 09:16:09 -0400
Chris Wedgwood <cw f00f org> wrote:
> On Sat, Jul 14, 2001 at 11:05:36PM -0700, John Alvord wrote:
>
> In the IBM solution to this (1977-78, VM/CMS) the critical data was
> written at the begining and the end of the block. If the two data
items
> didn't match then the block was rejected.
>
> Neat.
>
>
> Simple and effective. Presumably you can also checksum the block, and
> check that.
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.
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.
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