Re: [linux-lvm] LVM label lost / system does not boot

[Anthony Nelson <anthonyn@affinitygs.com>]

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Don't think I'm much of an expert in this area, but I had a similar 
issue that I worked through last week. I wasn't using mdadm, but I don't 
really think this is a situation that is really relevant to that.

I posted the question on serverfault and got enough help to get me 
through it. You can see it here:
http://serverfault.com/questions/275679/rescue-disk-is-unable-to-see-the-lvm-physical-volumes

The suggestion that got me on the right track seems to be very similar 
to your situation. How to recover your lvm configuration with mdadm.
http://www.howtoforge.com/recover_data_from_raid_lvm_partitions

The steps I went through were basically:
* Recover config using dd per steps in that article
* Recreate the physical volume using the same device
* Do a pvcfgrestore on the recovered config from step 1

That got me back up and running. I hope it helps.

Anthony Nelson
Affinity Global Solutions
701.223.3565 Ext: 13


On 6/5/2011 7:47 AM, Andreas Schild wrote:
> Hi
> The first part might sound like I am in the wrong group, but bear with 
> me...
> (I probably am, but I googled up and down RAID and LVM lists and I am 
> still  stuck):
> I have a software RAID 5 with 4 disks and LVM on top. I had one volume 
> group with two logical volumes (for root and data).
> I wanted to upgrade capacity and started by failing a drive, replacing 
> it with a bigger one and let the RAID resync. Worked fine for the 
> first disk. The second disk apparently worked (resynced, all looked 
> good), but after a reboot the system hung.
> After some back and forth with superblocks (on the devices, never on 
> the array) I was able to re-assemble the array clean.
> The system still does not reboot though: "Volume group "cmain" not found".
>
> I booted a live cd, assembled the array and did a pvck on the array 
> (/dev/md0):
> "Could not find LVM label on /dev/md0"
> pvdisplay /dev/md0 results in:
>   No physical volume label read from /dev/md0
>   Failed to read physical volume "/dev/md0"
>
> I do not have a backup of my /etc/ and therefore no details regarding 
> the configuration of the LVM setup (yes, I know...)
> All I have of the broken system is the /boot partition with its content
>
> Several questions arise:
> - Is it possible to "reconstitute" the LVM with what I have?
> - Is the RAID array really ok, or is it possibly corrupt to begin with 
> (and the reason no LVM labels are around)?
> - Should I try to reconstruct with pvcreate/vgcreate? (I shied away 
> from any *create commands to not make things worse.)
> - If all is lost, what did I do wrong and what would I need to backup 
> for a next time?
>
> Any ideas on how I could get the data back would greatly be 
> appreciated. I am in way over my head, so if somebody knowledgeable 
> tells me: "you lost, move on" would be bad, but at least would save me 
> some time...
>
> Thanks,
> Andreas
>
>
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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

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