Re: Superblock Missing

[David Mitchell <mr.david.mitchell@gmail.com>]

@Andreas Klauer a huge THANK YOU for taking the time to review my
issue.   I really appreciate your help.

Sincerely,

David Mitchell


On Mon, Sep 4, 2017 at 11:49 AM, Andreas Klauer
<Andreas.Klauer@metamorpher.de> wrote:
> On Sun, Sep 03, 2017 at 11:35:25PM -0400, David Mitchell wrote:
>> I really do NOT remember running the  --create command.
>
> There is no other explanation for it. It has happened somehow.
>
>> The pictures over 512k don't display correctly.
>
> So not only/necessarily a wrong data offset, but also wrong drive order.
>
>> At this point I'm hoping for help on next steps in recovery/troubleshooting.
>
> 1. Use overlays.
>
> https://raid.wiki.kernel.org/index.php/Recovering_a_failed_software_RAID#Making_the_harddisks_read-only_using_an_overlay_file
>
>    That way you can safely experiment and create RAID with
>    different settings. (Use --assume-clean and/or missing)
>
> 2. Check first 128M of each drive (your current data offset).
>    See if you can find a valid filesystem header anywhere.
>    That way you could determine the correct data offset.
>
> 3. Find a JPEG header (any known file type, like a 2-3M file)
>    and look at the other drives for the same offset. You should be
>    able to deduce RAID layout, chunksize, drive order from that.
>
> Instead of 3) you can also simply trial and error with overlays
> until you find a setting that allows photorec to find larger files intact.
>
> The resync might not necessarily have damaged your data. If the offsets
> were the same and the RAID level was the same, and the drives were in
> sync, a resync even with wrong settings would still produce the same data.
> For XOR, a ^ b = c and b ^ a = c so switching the drives does no damage
> provided you don't write anything else...
>
> Regards
> Andreas Klauer