Re: recovering from raid5 corruption

[NeilBrown <neilb@suse.de>]

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On Sun, 29 Apr 2012 18:38:29 -0400 Shaya Potter <spotter@gmail.com> wrote:

> somehow my raid5 got corrupted in the contexts of a main disk failure 
> (which wasn't raid related).
> 
> compounding this issue was that I had already had one disk in the raid5 
> go bad and was in the process of getting it replaced.
> 
> this raid array was 5 disks.
> 
> What I mean by corrupted is that the superblock of 3 of the remaining 4 
> devices seemed to have been wiped out (i.e. had a UUID of all 0s, though 
> still enough that it knew it was part of an md device)
> 
> now, the one whose superblock seems fine, places it at position disk 3 
> (of 0-4) and the missing disk at disk 2.
> 
> this would imply that there are only 6 permutations possible for the 
> other 3 disks.   (even if that assumptions is wrong, there are only 120 
> permutations possible, which I should easily be able to iterate over).
> 
> further compounding this, is that there were 2 LVM logical disks on the 
> physical raid device.
> 
> I've tried being cute and trying all 6 permutations to force recreate 
> the array, but lvm isn't picking up anything. (pvscan/lvscan/lvmdiskscan)
> 
> The original raid had a version of 0.90.00 (created in 2008), while the 
> new one has a version 1.20.
> 
> have I ruined any chances of recovery by shooting in the dark with my 
> cute attempts, am I SOL or is there a better/proper way I can try to 
> recover this data?
> 
> Luckily for me, I've been on a backup binge of late, but there still 
> about 500-1TB of stuff that wasn't backed up.

You've written a new superblock 4K in to each device, where previously here
was something.   So you have probably corrupted something though we cannot
easily tell what.

Retry your experiment with --metadata=0.90.  Hopefully one of those
combinations will work better.  If it does, make a backup of the data you
want to keep, then I would suggest rebuilding the array from scratch.

NeilBrown

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