Re: LVM label lost / system does not boot

Anthony Nelson <anthonyn@affinitygs.com> · Mon, 06 Jun 2011 08:27:34 -0500



    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 Âstuck):
      I have aÂsoftware 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:
        Â No physical volume label read from /dev/md0
        Â 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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