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

Björn Nadrowski bjrnfrdnnd at gmail.com
Wed Mar 27 12:47:43 UTC 2013

As I say, 
I do not think (maybe that is just a hope) that the offset did shift. 
I believe that because

* there are two complete vg descriptions in the same part at the beginning of the device, before and after my vgcreate action
* the older vg description has been replaced by the newer, actual one after the vgcreate action

I made absolutely sure that the failing device had been flagged as failed and removed via mdadm --remove. 
When I added the new drive, the raid10 only ran on three disks.

What do you think I should do?
restore the beginning of the device using the file md0.txt?
Then recreate the physical volume again using the -uuid switch?
But what then?

On Mar 27, 2013, at 5:29 , Stuart D Gathman <stuart at bmsi.com> wrote:

> On Mar 26, Stuart D Gathman transmitted in part:
>> Why has the offset shifted?  Possibilities:
>> 1) different md driver version on knoppix (although using an older
>> version would move the md superblock from end of drive to beginning of
>> drive - shifting the opposite way).  Or different options.  BUT mdadm
>> seemed to recognize your RAID, so let's
>> discount this theory.
>> 2) alignment options to pvcreate - but it still should have been seen by
>> lvs!
>> 3) the offset hasn't shifted, but you've written over the first few
>> sectors with the empty VG.  Is the 2nd human readable part, by any
>> chance, missing the first part?  You could post both parts for us to
>> look at.
> 4) the shape of the md array changed.  Say, you somehow didn't actually remove the failed drive before adding the replacement.  What
> does md raid10 do if you add a 4th disk to a 3 drive array?  Add
> it as a spare?  Reshape, shuffling all your data?
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