[TriLUG] how to restore lvm data

[Maxwell Spangler]

On Tue, 2010-04-13 at 20:43 -0400, Ralph Blach wrote:
> Ok, I made a bad mistake.  I accidentally deleted the partion table for 
>  a disk but the linux box still has the lvm data on it.
> 
> However system config lvm does not show a /dev/sdc where the lvm's  are 
> located.
> is there a way to recover /dev/sdc to show so that the lvm's are shown 
> on /dev/sdc

I'm working with LVM study over here and used my test disk to duplicate
and resolve your problem.

In my case I had a single 300GB maxtor drive with four partitions, two
of which (#1 and #3) were in use as part of a single volume group called
vg_maxtor.

I deleted each of those partitions to duplicate your situation.

Running # vgscan produced errors related to being unable to read disk
blocks from a device-mapper device dm-1.

I rebooted to further simulate the environment you described.

Then I downloaded testdisk (http://www.cgsecurity.org/wiki/TestDisk) and
ran that.

Testdisk let me select the physical drive being used for testing and
scan it from start to finish to find missing partitions.  It easily
found partitions 1 and 3 and let me write a new partition table
identical to the setup before this experiment.

I then ran # partprobe to let the kernel rescan for hard drive
partitions and in this case, it succeed.  Sometimes you just have to
reboot (and testdisk suggests this.)

Running # vgscan again with the partitions recovered found the vg_maxtor
volume group.

Next I re-activated the volume group with the vgchange command:

# vgchange -a y 

Then I was able to mount the two logical volumes containing ext4
filesystems that were contained within this volume group.

Please let us know if this process works for you.  I hadn't known how to
do this before and just learned it on the fly as part of studying LVM2,
so I enjoyed the opportunity.

-- 
Maxwell Spangler
========================================================================
        Linux, Unix and Database Administration
        Currently: Boulder, Colorado
        LinkedIn: http://www.linkedin.com/in/maxwellspangler