copy logical volume to another server

Question

I have copied a logical volume from Server A to Server B, using dd command, however every time I try to mount the volume

root@munin:~# mount /dev/DS/data_snap /mnt/
mount: you must specify the filesystem type

I tried using different options such as -t ext4 I get the following

root@munin:~# mount -t ext4 /dev/DS/data_snap /mnt/
mount: wrong fs type, bad option, bad superblock on /dev/mapper/DS-data_snap,
   missing codepage or helper program, or other error
   In some cases useful info is found in syslog - try
   dmesg | tail  or so

when I run dmesg | tail , I get the following

[ 3050.756552] EXT2-fs (dm-0): error: can't find an ext2 filesystem on dev dm-0.
[ 3141.079177] EXT4-fs (dm-0): VFS: Can't find ext4 filesystem

This is the result of fs check

root@munin:~# fsck.ext4 /dev/mapper/DS-data_snap
e2fsck 1.42 (29-Nov-2011)
fsck.ext4: Superblock invalid, trying backup blocks...
Error reading block 557056 (Invalid argument).  Ignore error<y>? cancelled!

/dev/mapper/DS-data_snap: Invalid argument while reading block 557056

/dev/mapper/DS-data_snap: Invalid argument reading journal superblock

fsck.ext4: Invalid argument while checking ext3 journal for /dev/mapper/DS-data_snap

/dev/mapper/DS-data_snap: ***** FILE SYSTEM WAS MODIFIED *****

/dev/mapper/DS-data_snap: ********** WARNING: Filesystem still has errors **********

Any ideas on how to fix this?

Answer 1

Was the source partition unounted or mounted read-only when you made the copy ?
You just can't copy an partition that is mounted write-able and expect it to work. You will have copied garbage.

Answer 2

I don't think I'd trust dd to copy a snapshot volume; it's much better to use a filesystem aware tool. I back my systems up by making LVM snapshots and copying the filesystems off with fsarchiver. I've had to restore twice and it worked well both times.