On Tue, Dec 30, 2008 at 11:30, Carsten Aulbert <carsten.aulb...@aei.mpg.de> wrote: > Hi Marc, > > Marc Bevand wrote: >> Carsten Aulbert <carsten.aulbert <at> aei.mpg.de> writes: >>> In RAID6 you have redundant parity, thus the controller can find out >>> if the parity was correct or not. At least I think that to be true >>> for Areca controllers :) >> >> Are you sure about that ? The latest research I know of [1] says that >> although an algorithm does exist to theoretically recover from >> single-disk corruption in the case of RAID-6, it is *not* possible to >> detect dual-disk corruption with 100% certainty. And blindly running >> the said algorithm in such a case would even introduce corruption on a >> third disk. >> > > Well, I probably need to wade through the paper (and recall Galois field > theory) before answering this. We did a few tests in a 16 disk RAID6 > where we wrote data to the RAID, powered the system down, pulled out one > disk, inserted it into another computer and changed the sector checksum > of a few sectors (using hdparm's utility makebadsector). The we > reinserted this into the original box, powered it up and ran a volume > check and the controller did indeed find the corrupted sector and > repaired the correct one without destroying data on another disk (as far > as we know and tested).
You are talking about diffrent types of errors. You tested errors that the disk can detect. That is not a problem on any RAID, that is what it is designed for. He was talking about errors that the disk can't detect (errors introduced by other parts of the system, writes to the wrong sector or very bad luck). You can simulate that by writing diffrent data to the sector, _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
