Monday, August 29, 2016

Restoring LVM Post-Install

I had to reinstall my linux operating system with an existing LVM over RAID. During the install I formatted one of the physical volumes PV. I used it for / (root), swap and /boot partitions. I could have used the existing Logical Volume LV for these but this device is also encrypted. I doubt I can reuse it without unlocking it. So I simply wiped it clean and made a clean install. After reboot I checked the status of the LVM and the RAID. Both are okay-ish. The RAID is clean according to mdadm. LVM informed me that the volume group is degraded. I'm missing a physical volume. I know I wiped it clean.

So how do I restore the volume group so I can get at my data.

LVM keeps its configuration files in /etc/lvm/backups and also in /etc/lvm/archives/"name-of-volume-group". So pick the current or latest one in /etc/lvm/backups or the older ones in /etc/lvm/archives/"volume-group". You need two things - the backup configuration file and the UUID of the physical volume. Using the terminal type:

#pvcreate --uuid UUID  --restorefile PATH-TO-THE-BACKUP-FILE-VOLUME-GROUP.VG /dev/sda

Unfortunately, I get an error message telling me that the Device is not found. (or ignored by filter). So I have to check the /etc/lvm.conf if by chance my device is simply being ignored or left out, simply not detected due to an uncommented line in the file.

I think in my case the physical volume was really wiped out, formatted, erased including the metadata. So, can I restore the volume group instead with the remaining physical volume? With the commands pvdisplay, vgdisplay and lvdisplay, it looks promising that I could. After consulting the man pages for vgreduce and vgchange I hit the terminal again.

#vgreduce --removemissing  ubuntu-vg

If you have data in the missing volumes, first try to salvage it. Afterwards, the remaining logical volumes are activated with this command:

#vgchange --activate y ubuntu-vg

Now check the status of your LVM with pvdisplay, vgdisplay and lvdisplay. My logical volumes now appear on the file manager, so that's a good sign I have saved the data.

--
Donato Roque @ubuntu-16-04
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