From mboxrd@z Thu Jan  1 00:00:00 1970
From: John Robinson <john.robinson@anonymous.org.uk>
Subject: Re: RAID6 data-check took almost 2 hours, clicking sounds, system
 unresponsive
Date: Wed, 13 Apr 2011 11:57:24 +0100
Message-ID: <4DA58194.4070403@anonymous.org.uk>
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To: Gavin Flower <gavinflower@yahoo.com>
Cc: NeilBrown <neilb@suse.de>, linux-raid@vger.kernel.org
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On 12/04/2011 22:30, Gavin Flower wrote:
> --- On Fri, 8/4/11, NeilBrown<neilb@suse.de>  wrote:
> [...]
>> No, it was clearly a disk-drive problem.
>> e.g.
>> Apr  7 14:42:12 saturn kernel: [231957.756023]
>> ata3.00: failed command: READ FPDMA QUEUED
>>
>> a READ command sent to a n 'ata' device failed.  i.e.
>> disk error.
> [...]
>
> Hi Neil,
>
> I think it is either a drive or cable problem.
>
> However, I was wondering if /proc/mdstat could list drives in a more consistent manner.  The C drive has dropped out and affected all 3 RAID partitions.  A quick look at /proc/mdstat suggests that md2&  md1 have the same drive drop out [UUUU_], but a different drive for md0 [UU_UU].  In fact, the list of drives (...sda4[0] sdc4[6](F)...) is not consistent with the [UUUU_] representation even for the same mdN!
>
> # date ; cat /proc/mdstat
> Wed Apr 13 08:40:09 NZST 2011
> Personalities : [raid6] [raid5] [raid4]
>
> md2 : active raid6 sda4[0] sdc4[6](F) sdd4[3] sdb4[5] sde4[1]
>        1114745856 blocks super 1.1 level 6, 512k chunk, algorithm 2 [5/4] [UUUU_]

This looks correct: sorting the first line into md slot order we have:
md2 : active raid6 sda4[0] sde4[1] sdd4[3] sdb4[5] sdc4[6](F)
which is UUUU_

> md1 : active raid6 sda2[0] sdc2[5](F) sdd2[3] sde2[2] sdb2[1]
>        307198464 blocks level 6, 512k chunk, algorithm 2 [5/4] [UUUU_]

Similarly:
md1 : active raid6 sda2[0] sdb2[1] sde2[2] sdd2[3] sdc2[5](F)
which is UUUU_

> md0 : active raid6 sda3[0] sdb3[4] sdd3[3] sdc3[5](F) sde3[1]
>        10751808 blocks level 6, 64k chunk, algorithm 2 [5/4] [UU_UU]

This one I don't get:
md0 : active raid6 sda3[0] sde3[1] sdd3[3] sdb3[4] sdc3[5](F)
which ought to be UUUU_ again...

Perhaps `mdadm -D /dev/md[0-2]` would make things clearer...

Cheers,

John.