Re: raid device gone underneath array

[NeilBrown <neilb@suse.de>]

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On Thu, 18 Oct 2012 18:01:34 -0600 Marcus Sorensen <shadowsor@gmail.com>
wrote:

> I've been using software raid to mirror two devices, and recently one
> of the drives went AWOL.
> 
> md1 : active raid1 sdm[0] sdc[1](F)
>       12884900728 blocks super 1.2 [2/1] [U_]
>       bitmap: 1/96 pages [4KB], 65536KB chunk
> 
> However, md1 froze, and in looking at the logs I saw this:
> 
> Oct 18 17:47:48 sys kernel: md: cannot remove active disk sdc from md1 ...
> Oct 18 17:47:48 sys kernel: md: cannot remove active disk sdc from md1 ...
> 
> [root(marcus)@sanmirror3-01 ~]# mdadm --manage /dev/md1 --remove /dev/sdc
> mdadm: cannot find /dev/sdc: No such file or directory
> 
> /dev/sdc was already gone! The /sys/block was already removed, no
> reference to it in /proc/scsi/scsi. So md1 was destined to sit there
> forever. So I rebooted and started up the degraded array.

These messages imply that 'sdc' was sent a request and no reply has been
received.  Until the count of pending requests hits zero, md cannot
completely release sdc, and if it was a write - cannot reply to the request
that it received from a files system.

When a device fails or disappears the driver should ensure that all pending
requests fail - and return that failure status.  md depends on this.
So - assuming this status continued for more than a minute - it looks like a
bug with the driver for 'sdc'.

NeilBrown


> 
> Using kernel 3.6.2 from kernel.org
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