Date: Mon, 22 Jul 2013 08:11:34 +0100 From: krad <kraduk@gmail.com> To: Daniel Feenberg <feenberg@nber.org> Cc: frank2@fjl.co.uk, Steve O'Hara-Smith <steve@sohara.org>, FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: to gmirror or to ZFS Message-ID: <CALfReyf1MfRy=c00w4-N0SdaKTtSzbgCrHH7%2BXJLYZ9_3acWdQ@mail.gmail.com> In-Reply-To: <Pine.GSO.4.64.1307201558490.29785@nber6> References: <4DFBC539-3CCC-4B9B-AB62-7BB846F18530@gmail.com> <alpine.BSF.2.00.1307152211180.74094@wonkity.com> <976836C5-F790-4D55-A80C-5944E8BC2575@gmail.com> <51E51558.50302@ShaneWare.Biz> <51E52190.7020008@fjl.co.uk> <CAOaKuAVULVuZxtExp=mNi-J7kMNbsxbLJVsv8nKTA0-Ru6M3%2Bw@mail.gmail.com> <6CE5718E-2646-4D8C-AF98-37384B8851C5@mac.com> <CAOaKuAU8nhaoq%2B6hCVkB%2Bb-ppiBvYPKANdWJRnYcmKaPdecwZA@mail.gmail.com> <DCC017BE-A293-4C1B-8B6F-D9AF6F50125B@mac.com> <51EAC56C.4030801@fjl.co.uk> <20130720201214.90206565e00675611996176d@sohara.org> <Pine.GSO.4.64.1307201558490.29785@nber6>
next in thread | previous in thread | raw e-mail | index | archive | help
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 <feenberg@nber.org> wrote: > > > On Sat, 20 Jul 2013, Steve O'Hara-Smith wrote: > > On Sat, 20 Jul 2013 18:14:20 +0100 >> Frank Leonhardt <frank2@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 <steve@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-** >> unsubscribe@freebsd.org <freebsd-questions-unsubscribe@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-** > unsubscribe@freebsd.org <freebsd-questions-unsubscribe@freebsd.org>" >
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CALfReyf1MfRy=c00w4-N0SdaKTtSzbgCrHH7%2BXJLYZ9_3acWdQ>