Broke my dmraid? Help please!

E-Razor · n00b Joined: 11 Jul 2004 Posts: 69

Hi all,

I'm having quite a serious problem.

Today my server hung and I rebooted it - without any luck. Since it's a root server I started the recovery image and tried to mount my root-partition.

I am using dmraid, and unfortunatelly started with:
mdadm --create --level=1 --disk-count=2 /dev/md0 /dev/sda2 /dev/sdb2

It tried to resync, and I had to reboot. After the reboot I tried with:
mdadm --assemble /dev/md0 /dev/sda2 /dev/sdb2

The resync took quite long and afterwards I'm still not able to mount /dev/md0 .

Kernel log is:

NeddySeagoon · Posted: Mon Jul 08, 2013 6:10 pm Post subject:

E-Razor,

mdadm --create is a very bad thing to do. It writes new raid metadata, which in effect, destroys your old raid. The sync won't have helped either.

However, all may not be lost. Creating new raid metadata is harmless *if* its identical to the old metadata. User data is not harmed in the process.
The downside is that mdadms defaults changed a few months ago, so if your original raid was a year or more old and you did not specify the parameters explicitly, you now have raid metadata version 1.2 but the old one was version 0.9.

So when did you create the old raid and how?

It gets slightly worse. Raid version 0.9 metadata is written at the end of the volume and the filesystem starts in the usual place, as if the volume is not a member of a raid set.
Raid version 1.2 metadata is written at the start of the volume and tramples over the primary extX filesystem superblock, that means you can no longer mount the filesystem using the primary superblock, which is what the standard invocation of mount does.

If we know what you used to have, something may be recoverable.

Your partition table would also be useful but I suppose that is inside the raid set and no longer available.
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Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

E-Razor · n00b Joined: 11 Jul 2004 Posts: 69

I think the versions are the same since it's also the same rescue image.

I created it about 1 year ago.

Fstab looks like this:

NeddySeagoon · Posted: Mon Jul 08, 2013 8:25 pm Post subject:

E-Razor,

If you allowed half the raid to mount rw, the two mirrors are now out of sync.
Recover what you can from /dev/sda2. Its very important that you do not write to a damaged raid/filesystem until you understand the damage.

I suspect you used to have raid superblock version 0.9 but now you have version 1.2
What does

E-Razor · n00b Joined: 11 Jul 2004 Posts: 69

I finally got it to work again.

Thanks for your hints!

I had version 0.9 and wrote "mdadm --create ..." which confused my system.

However, after e2fsck of one of the partions I was able to get my data back. I disconnected the working partition from the raid and formatted the raid again, then copied the old files into the empty raid-partiotion again.

My init was broken and I simply did a chroot and emerge which helped and the system is online now.

It seems I've had a lot of luck that the --create did not destroy the partition.

iandoug · Posted: Sun Sep 22, 2013 1:45 pm Post subject:

iandoug · Posted: Sun Sep 22, 2013 1:51 pm Post subject: would downgrading help?

would it help to dowgrade back to mdadm 3.1.4?
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Jaglover · Posted: Sun Sep 22, 2013 2:21 pm Post subject:

iandoug · Posted: Sun Sep 22, 2013 2:38 pm Post subject: solved