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

[NeilBrown <neilb@suse.de>]

On Fri, 5 Aug 2011 13:28:41 +0200 Aaron Scheiner <blue@aquarat.za.net> 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 <stan@hardwarefreak.com> wrote:
> > On 8/5/2011 5:04 AM, Aaron Scheiner wrote:
> >> 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.
> >
> > ...
> >> 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..
> >
> >> 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.
> >
> >> 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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