Re: On the subject of RAID-6 corruption recovery

["H. Peter Anvin" <hpa@zytor.com>]

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