Re: RAID MIA. Again. (Kinda.)

[Michael Evans <mjevans1983@gmail.com>]

On Fri, Mar 5, 2010 at 7:24 AM, Ken D'Ambrosio <ken@jots.org> wrote:
> On Thu, March 4, 2010 8:30 pm, Neil Brown wrote:
>> Try this:
>>
>>
>> cat /etc/fstab cat /etc/mdadm.conf mdadm -Esvv mdadm -Asv blkid -p /dev/md*
>>
>> And include all the output.
>
> See attached.  Note that fstab is essentially irrelevant; I'd mounted by
> hand, and was going to add the entry after I got the server back in the
> server room.
>
>> (sorry if I seem grumpy, but I'm a bit tired which makes it harder to
>> appear polite).
>
> Know what you mean; got four hours', myself, due to a virtualization
> migration.
>
> For the record, I've got my backup tapes ordered (again) -- if you can
> tell me what I did wrong, that would be almost as satisfying as getting
> the data back.
>
> Thanks,
>
> -Ken
> --
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>

Here's a stab at it. I've never tried to do it like this and haven't
glanced at the code so I can't be sure, but this seems to be the most
likely suspect:

#ARRAY /dev/md0 level=raid5 num-devices=4 devices=sda2,sdb2,sdd2,sdc2

Your commented out version seems to specify this mapping
0,sda2
1,sdb2
2,sdd2
3,sdc2

However the array is detected like this by uuid alone (I re-ordered
the entries so they're easier to read):

mdadm: /dev/sdb2 is identified as a member of /dev/md0, slot 0.
mdadm: /dev/sdc2 is identified as a member of /dev/md0, slot 1.
mdadm: /dev/sda2 is identified as a member of /dev/md0, slot 2.
mdadm: /dev/sdd2 is identified as a member of /dev/md0, slot 3.
mdadm: added /dev/sdb2 to /dev/md0 as 0
mdadm: added /dev/sdc2 to /dev/md0 as 1
mdadm: added /dev/sda2 to /dev/md0 as 2
mdadm: added /dev/sdd2 to /dev/md0 as 3
mdadm: /dev/md0 has been started with 4 drives.

This corresponds to:

0,sdb2
1,sdc2
2,sda2
3,sdd2

Note how the drives are out of order?  Thus the reason for  only using
UUID and NOT explicitly specifying an ordering?
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