From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: On the subject of RAID-6 corruption recovery
Date: Fri, 04 Jan 2008 16:03:57 -0800
Message-ID: <477EC96D.80505@zytor.com>
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To: Thiemo Nagel <thiemo.nagel@ph.tum.de>
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Thiemo Nagel wrote:
> 
> Inverting your argumentation, that means when we don't see z >= n or
> inconsistent z numbers, multidisc corruption can be excluded statistically.
> 
> For errors occurring on the level of hard disk blocks (signature: most
> bytes of the block have D errors, all with same z), the probability for
> multidisc corruption to go undetected is ((n-1)/256)**512.  This might
> pose a problem in the limiting case of n=255, however for practical
> applications, this probability is negligible as it drops off
> exponentially with decreasing n:
> 

That assumes fully random data distribution, which is almost certainly a 
false assumption.

	-hpa