> Thiemo Nagel wrote: >>>> 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. >> >> Agreed. This means, that the formula only serves to specify a lower >> limit >> to the probability. However, is there an argumentation, why a >> pathologic >> case would be probable, i.e. why the probability would be likely to >> *vastly* deviate from the theoretical limit? And if there is, would >> that >> argumentation not apply to other raid 6 operations (like "check") also? >> And would it help to use different Galois field generators at different >> positions in a sector instead of using a uniform generator? >> > > What you call "pathologic" cases when it comes to real-world data are > very common. It is not at all unusual to find sectors filled with only > a constant (usually zero, but not always), in which case your **512 > becomes **1. That's why I was asking about the generator. Theoretically, this situation might be countered by using a (pseudo-)random pattern of generators for the different bytes of a sector, though I'm not sure whether it is worth the effort. Kind regards, Thiemo Nagel - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
