Re: Possible data corruption after rebuild

[NeilBrown <neilb@suse.de>]

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On Fri, 6 Jul 2012 12:09:43 -0400 Alex <mysqlstudent@gmail.com> wrote:

> Hi,
> 
> I had a situation where after rebooting all three drives of a RAID5
> array were marked as spares. I rebuild the array using "mdadm -C
> /dev/md1 -e 1.1 --level 5 -n 3  --chunk 512 --assume-clean /dev/sda2
> /dev/sdb2 /dev/sdc2" and mdstat showed it was again assembled. The
> filesystem types on /dev/sdb were all "Linux" instead of "Linux raid
> autodetect", so I changed them back.

You've been bitten by http://neil.brown.name/blog/20120615073245

So md1 is all happy again is it?

> 
> /dev/md2 also has a problem, and I have no idea what to do there either.
> 
> When I tried to fsck it to be sure it was intact, it prompted me that
> there was a problem with the superblock, and I answered Yes to "Fix?".

Always use "fsck -n" to check if something is intact!!

> 
> After there being a number of further errors, I quit fsck, and am here for help.
> 
> Did I perhaps assemble the array in the wrong disk order? Is there
> another superblock that may be useful here and how would I find it?

Certainly possible.  With only 3 devices there aren't may different orders to
test so you could try them all.

As fsck thought it recognised a filesystem it is very likely that the first
device is correct, so just try swapping the other to and issuing a new
--create command.  Then "fsck -n".

NeilBrown


> 
> I'm really concerned that I've lost the data and really hope someone
> has some ideas.
> 
> # cat /proc/mdstat
> Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5]
> [raid4] [raid10]
> md1 : active raid5 sda2[0] sdc2[2] sdb2[1]
>       51196928 blocks super 1.1 level 5, 512k chunk, algorithm 2 [3/3] [UUU]
> 
> md2 : active raid5 sdc3[0] sdb3[2] sda3[1]
>       1890300928 blocks super 1.1 level 5, 512k chunk, algorithm 2 [3/3] [UUU]
> 
> md0 : active raid1 sdc1[0] sdb1[1]
>       255988 blocks super 1.0 [3/2] [U_U]
> 
> unused devices: <none>
> 
> # mdadm -E /dev/md1
> mdadm: No md superblock detected on /dev/md1.
> 
> # mdadm --detail /dev/md1
> /dev/md1:
>         Version : 1.1
>   Creation Time : Fri Jul  6 13:41:54 2012
>      Raid Level : raid5
>      Array Size : 51196928 (48.83 GiB 52.43 GB)
>   Used Dev Size : 25598464 (24.41 GiB 26.21 GB)
>    Raid Devices : 3
>   Total Devices : 3
>     Persistence : Superblock is persistent
> 
>     Update Time : Fri Jul  6 16:01:18 2012
>           State : clean
>  Active Devices : 3
> Working Devices : 3
>  Failed Devices : 0
>   Spare Devices : 0
> 
>          Layout : left-symmetric
>      Chunk Size : 512K
> 
>            Name : sysresccd:1  (local to host sysresccd)
>            UUID : 4ce6925e:b6cbd20e:7f3efbfc:668295fe
>          Events : 2
> 
>     Number   Major   Minor   RaidDevice State
>        0       8        2        0      active sync   /dev/sda2
>        1       8       18        1      active sync   /dev/sdb2
>        2       8       34        2      active sync   /dev/sdc2
> 
> Thanks for any ideas,
> Alex
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