Re: Grub-install, superblock corrupted/erased and other animals

On Fri, 5 Aug 2011 13:28:41 +0200 Aaron Scheiner [off-list ref] wrote:

"Wish I could have helped you recover the array.  When a patient comes
through emergency with 3 GSWs to the forehead and no pulse, there's
nothing that can be done.  :("

Quite an analogy :P . Is it really that hopeless ? And of interest
have you been in that situation ? I have the order of the array... so
it should just be a case of reconstructing it in the same way it was
created. Only one device was partitioned (as can be seen from the
dmesg logs) and that device is known.

Most of the array was backed up to another array, but there are some
photos I'd like to recover. The array doesn't need to be functional
any time soon (I'm happy to keep working on it for another 3 months if
necessary).

Besides, it's a good learning experience.

I "re-created" the array using the drive order I specified in the
previous e-mail, but replacing drive 9 with "missing". I then ran
xfs_check on the md device and it failed (as it did with every other
re-create attempt). I'll give your suggestion of xfs_repair -n a go :)

When you create the array, what 'data offset' does mdadm choose?
If not the same as the original the filesystem will of course not look right.

You might need to hack mdadm (super1.c) to set a different data_offset

NeilBrown

.

I'll have a look at the start of the md device with a hex editor and
see if there's anything interesting there.

On Fri, Aug 5, 2011 at 12:32 PM, Stan Hoeppner [off-list ref] wrote:

quoted

On 8/5/2011 5:04 AM, Aaron Scheiner wrote:

quoted

I followed your advice and ran a scalpel instance for every drive in
the array. The scanning process finished this morning yay (and
obviously went a lot faster).

Glad I could help.

...

quoted

So now the next step would have been to re-create the array and check

Unless Neil has some hex editor (or other similar) trick up his sleeve
that would allow you to manually recreate the sectors you hosed
installing grub..

quoted

if a file system check finds something... but because of the offsets
that probably won't work ?

If you are able to use the Force to assemble the disks in the correct
order, getting the raid device back up and running, then run 'xfs_repair
-n /dev/md0' to do the check.  The '-n' means "no modify".  xfs_repair
is better than xfs_check in many aspects.  They are two separate code
paths that serve the same function, but they behave a little differently
under the hood.

quoted

Thanks again :)

Wish I could have helped you recover the array.  When a patient comes
through emergency with 3 GSWs to the forehead and no pulse, there's
nothing that can be done.  :(

--
Stan

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