From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Evans Subject: Re: emergency call for help: raid5 fallen apart Date: Thu, 25 Feb 2010 18:42:51 -0800 Message-ID: <4877c76c1002251842g1a3b2f91ka7a825fd99a4ec18@mail.gmail.com> References: <4B853DB7.1060406@xunil.at> <20100224152228.GB11039@cthulhu.home.robinhill.me.uk> <4B85467C.5020008@xunil.at> <4B855621.5010000@xunil.at> <4B855987.1010605@xunil.at> <4B855B8C.8080802@xunil.at> <4B862F2C.5030302@texsoft.it> <4B86A943.3040804@anonymous.org.uk> <4B86C207.6030304@anonymous.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <4B86C207.6030304@anonymous.org.uk> Sender: linux-raid-owner@vger.kernel.org To: John Robinson Cc: Linux RAID List-Id: linux-raid.ids On Thu, Feb 25, 2010 at 10:31 AM, John Robinson wrote: > On 25/02/2010 17:41, Dawning Sky wrote: >> >> On Thu, Feb 25, 2010 at 8:45 AM, John Robinson >> wrote: >>> >>> On 25/02/2010 08:05, Giovanni Tessore wrote: >>> [...] >>> I do think we urgently need the hot reconstruction/recovery feature= , so >>> failing drives can be recovered to fresh drives with two sources of= data, >>> i.e. both the failing drive and the remaining drives in the array, = giving >>> us >>> two chances of recovering every sector. >> >> I was one of those 4 cases in the part month. =A0I would have certai= nly >> benefited from this when I tried to replace a failing drive on my ol= d >> raid-5. =A0But =A0I think actually the redundancy you desired can be >> achieved by running a raid-6 at the degraded mode (with 1 missing >> drive). >> >> Do I miss something? =A0If this is the case, shouldn't we all >> be doing this instead of using the raid-5? > > I think you must be missing something, yes. RAID-6 with one drive mis= sing > would have 2 chances of recovering each sector, but then so does RAID= -5 with > no drives missing. In either case, lose a drive and you need every se= ctor on > the remaining drives to be good to complete the reconstruction and ke= ep the > array up. > > Cheers, > > John. > > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid"= in > the body of a message to majordomo@vger.kernel.org > More majordomo info at =A0http://vger.kernel.org/majordomo-info.html > No, what they're saying is that often drives don't /totally/ fail. They have segments that go bad first, and we are often catching them in that state. To use the segments that /are/ successfully returned there is a good chance that multiple 'not full member' drive could provide a complete, or usefully very near complete with known 'dead' areas set to store on fresh devices. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html