Re: [PATCH] 64 bit scsi read/write

Chris Wedgwood
2001-07-15T14:50:14Z

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