Re: RAID 5 array recovery - two drives errors in external enclosure

["Majed B." <majedb@gmail.com>]

Before creating the array, did you re-examine the disks with mdadm and
made sure of each disk's position in the array?

After your recabling, the disk names may have changed again.

mdadm --examine /dev/sdb1

      Number   Major   Minor   RaidDevice State
this     7       8       17        7      active sync   /dev/sdb1

   0     0       8      113        0      active sync   /dev/sdh1
   1     1       8       97        1      active sync   /dev/sdg1
   2     2       0        0        2      faulty removed
   3     3       0        0        3      faulty removed
   4     4       8       33        4      active sync   /dev/sdc1
   5     5       8       65        5      active sync   /dev/sde1
   6     6       8       49        6      active sync   /dev/sdd1
   7     7       8       17        7      active sync   /dev/sdb1

(That's the output of an array I'm working on)

Notice the first line: *this* and then the value of RaidDevice. That's
the position of the partition in the array. 0 is first, 1 is second,
and so on.

In my case, the order is: sdh1,sdg1,missing,missing,sdc1,sde1,sdd1,sdb1

On Fri, Sep 18, 2009 at 2:11 AM, Tim Bostrom <tbostrom@gmail.com> wrote:
> I re-cabled the drives so that they show up as the same drive letter
> as they were before when in the enclosure.
>
> I then went ahead and tried your idea of restarting the array. I tried
> this first:
>
> mdadm -C /dev/md0 -l 5 -n 5 -c 256 /dev/sd[bcde]1 missing
>
> mount -o ro /dev/md0 /mnt/teradata
>
> /var/log/messages:
> -----------------
> Sep 17 16:07:09 tera kernel: md: bind<sdb1>
> Sep 17 16:07:09 tera kernel: md: bind<sdc1>
> Sep 17 16:07:09 tera kernel: md: bind<sdd1>
> Sep 17 16:07:09 tera kernel: md: bind<sde1>
> Sep 17 16:07:09 tera kernel: raid5: device sde1 operational as raid disk 3
> Sep 17 16:07:09 tera kernel: raid5: device sdd1 operational as raid disk 2
> Sep 17 16:07:09 tera kernel: raid5: device sdc1 operational as raid disk 1
> Sep 17 16:07:09 tera kernel: raid5: device sdb1 operational as raid disk 0
> Sep 17 16:07:09 tera kernel: raid5: allocated 5268kB for md0
> Sep 17 16:07:09 tera kernel: raid5: raid level 5 set md0 active with 4
> out of 5 devices, algorithm 2
> Sep 17 16:07:09 tera kernel: RAID5 conf printout:
> Sep 17 16:07:09 tera kernel: --- rd:5 wd:4
> Sep 17 16:07:09 tera kernel: disk 0, o:1, dev:sdb1
> Sep 17 16:07:09 tera kernel: disk 1, o:1, dev:sdc1
> Sep 17 16:07:09 tera kernel: disk 2, o:1, dev:sdd1
> Sep 17 16:07:09 tera kernel: disk 3, o:1, dev:sde1
> Sep 17 16:07:56 tera kernel: EXT3-fs error (device md0):
> ext3_check_descriptors: Block bitmap for group 8064 not in group
> (block 532677632)!
> Sep 17 16:07:56 tera kernel: EXT3-fs: group descriptors corrupted!
> --------------------------------
>
>
> I then tried a few more permutations of the command:
> mdadm -C /dev/md0 -l 5 -n 5 -c 256 /dev/sd[bdce]1 missing
> mdadm -C /dev/md0 -l 5 -n 5 -c 256 /dev/sd[bdec]1 missing
> mdadm -C /dev/md0 -l 5 -n 5 -c 256 /dev/sd[becd]1 missing
>
> Every time I changed the order, it would still print the order the
> same in the log:
>
> Sep 17 16:02:52 tera kernel: md: bind<sdb1>
> Sep 17 16:02:52 tera kernel: md: bind<sdc1>
> Sep 17 16:02:52 tera kernel: md: bind<sdd1>
> Sep 17 16:02:52 tera kernel: md: bind<sde1>
> Sep 17 16:02:52 tera kernel: raid5: device sde1 operational as raid disk 3
> Sep 17 16:02:52 tera kernel: raid5: device sdd1 operational as raid disk 2
> Sep 17 16:02:52 tera kernel: raid5: device sdc1 operational as raid disk 1
> Sep 17 16:02:52 tera kernel: raid5: device sdb1 operational as raid disk 0
> Sep 17 16:02:52 tera kernel: raid5: allocated 5268kB for md0
> Sep 17 16:02:52 tera kernel: raid5: raid level 5 set md0 active with 4
> out of 5 devices, algorithm 2
> Sep 17 16:02:52 tera kernel: RAID5 conf printout:
> Sep 17 16:02:52 tera kernel: --- rd:5 wd:4
> Sep 17 16:02:52 tera kernel: disk 0, o:1, dev:sdb1
> Sep 17 16:02:52 tera kernel: disk 1, o:1, dev:sdc1
> Sep 17 16:02:52 tera kernel: disk 2, o:1, dev:sdd1
> Sep 17 16:02:52 tera kernel: disk 3, o:1, dev:sde1
>
>
>
> Am I doing something wrong?
>
>
>
>
> On Thu, Sep 17, 2009 at 2:22 PM, Robin Hill <robin@robinhill.me.uk> wrote:
>> On Thu Sep 17, 2009 at 01:42:30PM -0700, Tim Bostrom wrote:
>>
>>> OK,
>>>
>>> Let me start off by saying - I panicked.  Rule #1 - don't panic.  I
>>> did.  Sorry.
>>>
>>> I have a RAID 5 array running on Fedora 10.
>>> (Linux tera.teambostrom.com 2.6.27.30-170.2.82.fc10.i686 #1 SMP Mon
>>> Aug 17 08:38:59 EDT 2009 i686 athlon i386 GNU/Linux)
>>>
>>> 5 drives in an external enclosure (AMS eSATA Venus T5).  It's a
>>> Sil4726 inside the enclosure running to a Sil3132 controller via eSATA
>>> in the desktop.  I had been running this setup for just over a year.
>>> Was working fine.   I just moved into a new home and had my server
>>> down for a while  - before I brought it back online, I got a "great
>>> idea" to blow out the dust from the enclosure using compressed air.
>>> When I finally brought up the array again, I noticed that drives were
>>> missing.  Tried re-adding the drives to the array and had some issues
>>> - they seemed to get added but after a short time of rebuilding the
>>> array, I would get a bunch of HW resets in dmesg and then the array
>>> would kick out drives and stop.
>>>
>> <- much snippage ->
>>
>>> I popped the drives out of the enclosure and into the actual tower
>>> case and connected each of them to its own SATA port.  The HW resets
>>> seemed to go away, but I couldn't get the array to come back online.
>>>  Then I did the stupid panic (following someone's advice I shouldn't
>>> have).
>>>
>>> thinking I should just re-create the array, I did:
>>>
>>> mdadm --create /dev/md0 --level=5 --raid-devices=5 /dev/sd[b-f]1
>>>
>>> Stupid me again - ignores the warning that it belongs to an array
>>> already.  I let it build for a minute or so and then tried to mount it
>>> while rebuilding... and got error messages:
>>>
>>> EXT3-fs: unable to read superblock
>>> EXT3-fs: md0: couldn't mount because of unsupported optional features
>>> (3fd18e00).
>>>
>>> Now - I'm at a loss.  I'm afraid to do anything else.   I've been
>>> viewing the FAQ and I have a few ideas, but I'm just more freaked.  Is
>>> there any hope?  What should I do next without causing more trouble?
>>>
>> Looking at the mdadm output, there's a couple of possible errors.
>> Firstly, your newly created array has a different chunksize than your
>> original one.  Secondly, the drives may be in the wrong order.  In
>> either case, providing you don't _actually_ have any faulty drives, then
>> it should be (mostly) recoverable.
>>
>> Given the order you specified the drives in the create, sdf1 will be the
>> partition that's been trashed by the rebuild, so you'll want to leave
>> that out altogether for now.
>>
>> You need to try to recreate the array with the correct chunk size and
>> with the remaining drives in different orders, running a read-only
>> filesystem check each time until you find the correct order.
>>
>> So start with:
>>    mdadm -C /dev/md0 -l 5 -n 5 -c 256 /dev/sd[bcde]1 missing
>>
>> Then repeat for every possible order of the four disks and "missing",
>> stopping the array each time if the mount fails.
>>
>> When you've finally found the correct order, you can re-add sdf1 to get
>> the array back to normal.
>>
>> HTH,
>>    Robin
>> --
>>     ___
>>    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
>>   / / )      | Little Jim says ....                            |
>>  // !!       |      "He fallen in de water !!"                 |
>>
>
>
>
> --
> -tim
> --
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-- 
       Majed B.
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