But then zfs doesn't access every block on the disk does it, only the allocated ones
On 20 July 2013 21:07, Daniel Feenberg <feenb...@nber.org> wrote: > > > On Sat, 20 Jul 2013, Steve O'Hara-Smith wrote: > > On Sat, 20 Jul 2013 18:14:20 +0100 >> Frank Leonhardt <fra...@fjl.co.uk> wrote: >> >> It's worth noting, as a warning for anyone who hasn't been there, that >>> the number of times a second drive in a RAID system fails during a >>> rebuild is higher than would be expected. During a rebuild the remaining >>> drives get thrashed, hot, and if they're on the edge, that's when >>> they're going to go. And at the most inconvenient time. Okay - obvious >>> when you think about it, but this tends to be too late. >>> >> >> Having the cabinet stuffed full of nominally identical drives >> bought at the same time from the same supplier tends to add to the >> probability that more than one drive is on the edge when one goes. It's a >> pity there are now only two manufacturers of spinning rust. >> > > Often this is presummed to be the reason for double failures close in > time, also common mode failures such as environment, a defective power > supply or excess voltage can be blamed. I have to think that the most > common "cause" for a second failure soon after the first is that a failed > drive often isn't detected until a particular sector is read or written. > Since the resilvering reads and writes every sector on multiple disks, > including unused sectors, it can "detect" latent problems that may have > existed since the drive was new but which haven't been used for data yet, > or have gone bad since the last write, but haven't been read since. > > The ZFS scrub processes only sectors with data, so it provides only > partial protection against double failures. > > Daniel Feenberg > NBER > > > > >> -- >> Steve O'Hara-Smith <st...@sohara.org> >> ______________________________**_________________ >> freebsd-questions@freebsd.org mailing list >> http://lists.freebsd.org/**mailman/listinfo/freebsd-**questions<http://lists.freebsd.org/mailman/listinfo/freebsd-questions> >> To unsubscribe, send any mail to "freebsd-questions-** >> unsubscr...@freebsd.org <freebsd-questions-unsubscr...@freebsd.org>" >> >> ______________________________**_________________ > freebsd-questions@freebsd.org mailing list > http://lists.freebsd.org/**mailman/listinfo/freebsd-**questions<http://lists.freebsd.org/mailman/listinfo/freebsd-questions> > To unsubscribe, send any mail to "freebsd-questions-** > unsubscr...@freebsd.org <freebsd-questions-unsubscr...@freebsd.org>" > _______________________________________________ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"
