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SubjectRe: [PATCH] 64 bit scsi read/write
Chris Wedgwood <> 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
> 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:

Unfortunately, it's also patented:

Perhaps IBM will clarify their position with respect to free software and
patents in the upcoming conference.

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