From mboxrd@z Thu Jan 1 00:00:00 1970 From: Goswin von Brederlow Subject: Re: Question about raid robustness when disk fails Date: Wed, 27 Jan 2010 16:34:30 +0100 Message-ID: <87fx5r36k9.fsf@frosties.localdomain> References: <1262972385.8962.159.camel@kije> <87hbqeyua9.fsf@frosties.localdomain> <7d86ddb91001261619kbb77697t2660e5b8cc44535d@mail.gmail.com> <4877c76c1001262022p369eac60s639d87cad743ff94@mail.gmail.com> <87vden2a2a.fsf@frosties.localdomain> <4B6005DC.7070701@shiftmail.org> <87wrz3zvwu.fsf@frosties.localdomain> <4B6018EC.7090805@shiftmail.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <4B6018EC.7090805@shiftmail.org> (asdo@shiftmail.org's message of "Wed, 27 Jan 2010 11:43:56 +0100") Sender: linux-raid-owner@vger.kernel.org To: Asdo Cc: Goswin von Brederlow , linux-raid List-Id: linux-raid.ids Asdo writes: > Goswin von Brederlow wrote: >>> Is it possible to cancel a SATA/SCSI command that is being executed by >>> the drive? >>> (it's probably feasible only with NCQ disabled anyway, but it's easy >>> to disable NCQ) >>> >> >> Do you want to do that? I would rather have the drive keep trying and >> return an error if it can't read so the raid layer rewrites the blocks >> causing it to be remapped. I do not want to wait for that but I want it >> to happen. >> > So you want that to happen in the background? > Not that much benefit for that to happen in the background, imho. > Why not just having an error returned after a timeout, and normal MD > read-error-recovery procedure kicking in? (recomputation from parity > and rewrite of the damaged block) Because the drive might just had a seek error and needs to reposition its head. It might have been accessed on another partition and have a read error there taking time. Or just multiple reads on the partition. The drive taking long doesn't mean THIS read is broken. If you kick of a read-error-recovery and get another error on another drive then your raid will be down as well. Better not risk that. >>> It's a pity we have to rely on TLER, this narrows the choice of drives >>> a lot... >>> >> >> I don't. I just acknowledge the limitation and accept the downtime > The time might be so long that MD or the controller can drop the > entire drive. > It didn't happen to me but I think I read something like this on this ML... Downtime as in I had to shut down the system hard and remove a drive at a time till it would boot again when I came home in the evening. If it just hangs for 5 minutes till it kicks a drive but then continious running I still call that a success. >> to >> find and remove a broken but not properly failed disk. I use raid so I >> don't loose my data when a disk fails, not primarily for availability. >> So far I had one case in 10 years where a failing disk took down my >> system. >> MfG Goswin