From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Janos Haar" Subject: Re: questions about softraid limitations Date: Sun, 18 May 2008 23:51:40 +0200 Message-ID: <092d01c8b935$180cdac0$9300a8c0@dcccs> References: <002801c8b55a$60e4a360$0404a8c0@dcccs> <482AC2BB.5010602@dgreaves.com> <01be01c8b61a$6e616260$9300a8c0@dcccs> <482D479F.3040809@dgreaves.com> <022401c8b739$5262ba80$9300a8c0@dcccs> <482FF2DB.9060604@dgreaves.com> <07b301c8b8d7$f3e6d590$9300a8c0@dcccs> <48302861.3010607@dgreaves.com> Mime-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-2"; reply-type=original Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: David Greaves Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids ----- Original Message ----- From: "David Greaves" To: "Janos Haar" Cc: Sent: Sunday, May 18, 2008 3:00 PM Subject: Re: questions about softraid limitations > Janos Haar wrote: >> The actually best way is this: >> >> blockdev --setro /dev/SOURCE >> blockdev --setra 0 /dev/SOURCE >> ddrescue -v -b 4096 -B 1024 -e 1 -y 0 /dev/SOURCE /dev/TARGET (if you >> dont use a real clean disk with full of zeros, you need the -A option >> too) >> >> + need some kernel patch to disable all retry on the source disk. > Is that something you could share? Aaa, i made it myself about 1 year before on 2.6.18, but unfortunately at the moment the source is already deleted, and i dont save the diff. :-( I am not a good C programmer, but takes about 1 hour. ;-) > > It sounds like something that would be worth including in the libata error > handling to be controlled by something like > /sys/block/sdX/device/ioerr_retry_count This is a great idea! :) But not just for the ide drives! I think this is good for all block device! (usb, scsi, ide, sata...) Oops. And an old problem comes again: On IDE drives with read errors, sometimes drop the DMA. My script can be re-enable it sometimes, but not the real good solution.... If this can be fixed too, this will be great! :-) > > I'd be interested in playing with it and sending to Tejun Heo if you don't > have > time. > >> The best recovery history is in 3 steps: >> > [snip] >> >> There is no easy solution. :-( > > OK - I'll put this up on the wiki sometime. > >>> Hmm - I wonder if things like ddrescue could work with the md bitmaps >>> to improve >>> this situation? >>> Is this related to David Lethe's recent request? >> >> I think ddrescue is for copy/rescue the data, not for processing it. >> But can log the errors... ;-) > Yes - I meant to take the ddrescue output and manipulate the bitmap on the > copied drive to mark certain parts as 'bad'. > Ideally this could be done in the event of a dual-failure so that you > could > re-add 2 failed drives and the bitmaps could indicate. > > This may requires something closer to a bytemap but... This is good in this way. :-) Cheers, Janos > > > David