Physical Volume Metadata recovery

Andersonian · 10-06-2008, 06:19 PM

Hello,

I would really appreciate help on recovering some data.

I have a RAID1 array under /dev/md0 composed of devices /dev/sdb and /dev/sdc. I had lvm on the raid with 3 lv, the last of which was a snapshot partition.

My / is on /dev/sda. Recently, I reinstalled the system (Debian lenny) and reconfigured /dev/sda with lvm.
When I booted, the system correctly determined the presence of the RAID array and even activated it. All I had to do is import /dev/md0 back into the system.

However, out of stupidity, I ran

Code:

sudo pvcreate -v /dev/md0
    Set up physical volume for "/dev/md0" with 488396928 available sectors
    Zeroing start of device /dev/md0
  Physical volume "/dev/md0" successfully created

As it says, it overwrote the start of the device, the data is has not been affected. Now I don't know how to access the LVs on /dev/md0.

Does anyone have any suggestions on how to recover the Physical Volume Metadata of /dev/md0 ?

I do not have the backup file of the volume group on the raid, as I just reinstalled the system over it. Otherwise I would have just followed the instructions here.

Thank you in advance.

juanbobo · 10-09-2008, 02:27 PM

You might be able to restore the data with the testdisk utility.

Andersonian · 10-20-2008, 11:53 PM

I've made some progress. Here's a summary of my steps so far:

# Searched for lvm config

Code:

sudo dd if=/dev/sdb bs=512 count=255 skip=1 of=/temp.txt

# Filtered the output, saved the file to /etc/lvm/backup/data-raid
# Extracted the UID of pv0 (/dev/md0) and ran

Code:

pvcreate -ff -v -u JgOakP-gVVs-SfhX-lEXi-x4fQ-3gXz-3d17FN /dev/md0

# Restored lvm w/

Code:

vgcfgrestore -f /etc/lvm/backup/data-raid data-raid

# Imported the volume group with

Code:

vgimport data-raid

# Brought it up

Code:

vgchange -ay data-raid

Code:

# ls -l /dev/mapper
total 0
crw-rw---- 1 root root  10, 60 2008-10-11 20:16 control
brw-rw---- 1 root disk 253,  7 2008-10-19 10:12 data--raid-user
brw-rw---- 1 root disk 253,  4 2008-10-19 10:12 data--raid-media
brw-rw---- 1 root disk 253,  3 2008-10-19 10:12 data--raid-media-real
brw-rw---- 1 root disk 253,  6 2008-10-19 10:12 data--raid-snap--media
brw-rw---- 1 root disk 253,  5 2008-10-19 10:12 data--raid-snap--media-cow

# Tried mounting w/ following fstab conf

Code:

/dev/mapper/data--raid-media	/media/Pictures	reiserfs	defaults,noatime	0	0

it failed with

Code:

[630884.179103] ReiserFS: dm-3: warning: sh-2021: reiserfs_fill_super: can not find reiserfs on dm-3

There are supposed to be 2 volumes with data, data--raid-media a ReiserFS partition, and data--raid-user a LUKS encrypted one and a snapshot volume of the media partition.

Any ideas what could have gone wrong?