[linux-lvm] vg disappeared after replacing disc in raid10

[Stuart D Gathman]

Long ago, Nostradamus foresaw that on 03/25/2013 10:04 AM, Björn
Nadrowski would write:
> After replacing a disc in my raid10 system (ubuntu 12.04), my volume group (that contained all my data and my system) was gone.
>
> Problem description is here:
>
> http://ubuntuforums.org/showthread.php?t=2128504
>
> I managed to retrieve the metadata of the volume group and the logical volumes underneath, but I did not succeed using
>
> vgcfgrestore 
>
> successfully in order to regain access to my data.
>
> It seems I might have to try dmsetup, but I am afraid I might destroy my data if I use it. I have no experience with that program.
>
No immediate help, but I would have been more paranoid under knoppix,
and checked for the volume group (vgscan) *before* failing the bad disk,
and *before* adding the replacement.  Running pvs at those points would
be advisable also.

I just installed a customer system with raid10, so I am *very*
interested in what went wrong.  I have only used raid1 to this point,
and have been *very* impressed with the improved performance of 4 disks
with raid10 vs. 2 with raid1. 

Here is a theory to toss out:  raid10 on 3 disks can tolerate only 1
disk failure.  Maybe there were 2?  Maybe replaced the wrong drive? 

Does pvs show the raid10 drive as a PV?  There is no point trying to use
vgcfgrestore until you have some PVs to restore it to.
Where did you find the metadata?  From a backup?  From the beginning of
the raid10 drive?