Hi Mikael,
I did look through the archives and also at that recovery wiki and
permute script, but I think my case is different, even though I'm sure
others must have also hit it before. My problem isn't that I don't
know the order of the disks in the array, but that the data in the
array has been scrambled. As an example, if a given extent in the
array was ordered across the disks as so:
A B C P Q
where:
P = A ^ B ^ C
Q = A ^ mul(B) ^ mul(mul(C))
Then when my array was reconfigured in the incorrect order (say, with
disk 2 moved to the end), the layout was reordered to became:
A C P Q B
Then when the array was recreated in this state, the parity
information was recalculated such that the data on disk became:
A C P P' Q'
where:
P' = A ^ C ^ P
Q' = A ^ mul(C) ^ mul(mul(P))
Thus, the new parity information is now a function of two out of three
of the original data chunks (A and C) and one of the original parity
chunks (P), with data chunk B having been overwritten.
I need to reverse these disk writes across then entire length of the
array, after which I can reassemble the array in the correct order.
Thanks,
Steven
On Sat, Jul 18, 2015 at 3:33 PM, Mikael Abrahamsson <swmike@xxxxxxxxx> wrote:
> On Sat, 18 Jul 2015, Steven Reddie wrote:
>
>> I'm kind of hoping that all of this might have already been done, so
>> any pointers would be appreciated.
>
>
> https://raid.wiki.kernel.org/index.php/RAID_Recovery
> https://raid.wiki.kernel.org/index.php/Permute_array.pl
>
> There have historically been lots of threads here with people having the
> same problems, so if you search the archives for things like "assume-clean",
> "order", "mdadm", "create", "superblock", you'll find multiple examples of
> people actually successfully getting out of the problem you're also having.
>
> --
> Mikael Abrahamsson email: swmike@xxxxxxxxx
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