Re: Help recovering from failed disk on RAID 6

["Pascal Charest" <pascal.charest@gmail.com>]

Hum. Why not simply use the "fail" option to "fail" and thus put
offline the problematic drive ?

mdadm --fail /your/raid/device /the/drive/you/want/to/fail

You can "remove" the drive afterward with the "remove" command ;-). I
don't think you should do any "physical" operation like disconnecting
power supply of a live disk - even if it is a dodgy disk. "This
eliminates possibility that the bad disk will lock up the system" but
"create the possibility of a short circuit and having no more system
at all".

Pascal Charest


-- 
Pascal Charest, Free software consultant {GNU/Linux}
http://blog.pacharest.com

On Tue, May 13, 2008 at 12:28 PM, David Lethe <david@santools.com> wrote:
> I would also add to Steve's suggestion that you be prepared to
>  immediately disconnect the power to the dodgy disk once the rebuild
>  starts.  That eliminates possibility that the bad disk will lock up the
>  system.
>
>  David
>
>
>  -----Original Message-----
>  From: linux-raid-owner@vger.kernel.org
>
>
> [mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Steve Fairbairn
>  Sent: Tuesday, May 13, 2008 11:11 AM
>  To: 'Joshua Johnson'; linux-raid@vger.kernel.org
>  Subject: RE: Help recovering from failed disk on RAID 6
>
>  Hi,
>
>  It appears noone else has answered, so I'll try.  First I'd attempt to
>  start the array with the --force parameter, which I believe will start
>  the dirty array without the failed drive in it.
>
>  The other option to try depends on how long you have before the OS
>  freezes, but is to start the array with the dodgy drive in it, but
>  immediately tell mdadm to fail the dodgy disk.  This should have mdadm
>  start a resync with the spare drive.
>
>  Hope this helps,
>
>  Steve.
>
>  > -----Original Message-----
>  > From: linux-raid-owner@vger.kernel.org
>  > [mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Joshua Johnson
>  > Sent: 28 April 2008 03:17
>  > To: linux-raid@vger.kernel.org
>  > Subject: Help recovering from failed disk on RAID 6
>  >
>  >
>  > I am running a linux server with an 8 disk IDE/SATA RAID 6
>  > array.  One of the disks is having a problem which caused the
>  > machine to freeze. If I boot the machine without the problem
>  > disk the array fails to start.  If I boot with the problem
>  > disk the array starts correctly and begins syncing, but the
>  > machine will soon freeze up again when the disk drops out.
>  > My number one question is how to get the array back online.
>  > It has a spare disk, but since the OS is freezing rather than
>  > failing the disk that is having the problem, it never
>  > switched to the new disk.  When I try to start the array
>  > without the problem disk, I
>  > get:
>  >
>  > #mdadm --manage --run /dev/md0
>  > raid5: device hda2 operational as raid disk 0
>  > raid5: device sdb2 operational as raid disk 7
>  > raid5: device sda1 operational as raid disk 6
>  > raid5: device hdi2 operational as raid disk 5
>  > raid5: device hdg2 operational as raid disk 3
>  > raid5: device hde2 operational as raid disk 2
>  > raid5: device hdk2 operational as raid disk 1
>  > raid5: cannot start dirty degraded array for md0
>  > RAID5 conf printout:
>  >  --- rd:8 wd:7
>  >  disk 0, o:1, dev:hda2
>  >  disk 1, o:1, dev:hdk2
>  >  disk 2, o:1, dev:hde2
>  >  disk 3, o:1, dev:hdg2
>  >  disk 5, o:1, dev:hdi2
>  >  disk 6, o:1, dev:sda1
>  >  disk 7, o:1, dev:sdb2
>  > raid5: failed to run raid set md0
>  > md: pers->run() failed ...
>  > mdadm: failed to run array /dev/md0: Input/output error
>  >
>  > /proc/mdstat contains:
>  > Personalities : [raid1] [raid6] [raid5] [raid4]
>  > md1 : active raid1 hdg1[1] hda1[0]
>  >       4200896 blocks [2/2] [UU]
>  >
>  > md0 : inactive hda2[0] sdc2[8](S) sdb2[7] sda1[6] hdi2[5]
>  > hdg2[3] hde2[2] hdk2[1]
>  >       1529265920 blocks
>  >
>  >
>  > So how do I get this array to run?  I can't start it without
>  > the problem disk and I can't sync it with the problem disk.
>  > I am running RAID 6 to be able to recover from multiple disk
>  > failures so it is a little vexing that a single disk going
>  > offline renders my array unrunnable.  Any help with this
>  > issue is greatly appreciated.
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-- 
Pascal Charest, Free software consultant {GNU/Linux}
http://blog.pacharest.com