HOWTO: Relocate LVM to a New Server

The main storage on my home server is on 2 x 2TB hard disk drives which are configured as an LVM volume.

(For a guide on configuring LVM from scratch see this article.)

My server currently runs Ubuntu 10.04 but I've decided to bite the bullet and swap it over to Debian Squeeze.

I've never moved an LVM volume to another server / OS installation so it's time to learn how to do it, I guess.

Note:

It should be obvious but I will nevertheless say it here anyway. Mucking about with file-systems is a dangerous thing to do and any misstep can lead to disastrous, catastrophic and permanent DATA LOSS! Ensure that you have adequate backups before attempting this procedure. You have been warned!

First, you need to login as root.

sudo -i

Get the details for your current LVM Volume Group(s);

vgdisplay
  --- Volume group ---
  VG Name               store
  System ID             
  Format                lvm2
  Metadata Areas        2
  Metadata Sequence No  6
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                1
  Open LV               0
  Max PV                0
  Cur PV                2
  Act PV                2
  VG Size               3.64 TiB
  PE Size               4.00 MiB
  Total PE              953862
  Alloc PE / Size       953862 / 3.64 TiB
  Free  PE / Size       0 / 0   
  VG UUID               9zwhOn-3Qs6-aPTo-kqQ4-RL4p-ICTA-l56Dsz

As you can see, I have a single volume group called "store".

Let's see what Logical Volumes are in the Volume Group;

lvdisplay
  --- Logical volume ---
  LV Name                /dev/store/archive
  VG Name                store
  LV UUID                80eFYi-n0Z7-9br1-bbfg-1GQ6-Orxf-0wENTU
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                3.64 TiB
  Current LE             953862
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           254:0

We can see that there is a single volume 'archive' in the group.

Check your fstab for the line pertaining to your LVM volume;

cat /etc/fstab

The relevant line in my case is this;

UUID=057272e5-8b66-461a-ad18-c1c198c8dcdd /store/archive ext3 errors=remount-ro 0 1

Make sure you keep this info at hand for later on.

It so happens that I am sharing this volume using NFS so I need to stop my NFS server;

service nfs-kernel-server stop

so that I can unmount it.

umount /store/archive/

Now I need to mark the VG as inactive;

vgchange -an store
  0 logical volume(s) in volume group "store" now active

Next I prepare the volume group to be moved by "exporting" it;

vgexport store
  Volume group "store" successfully exported

Let's take another look at the volume group details;

vgdisplay
  Volume group store is exported
  --- Volume group ---
  VG Name               store
  System ID             
  Format                lvm2
  Metadata Areas        2
  Metadata Sequence No  5
  VG Access             read/write
  VG Status             exported/resizable
  MAX LV                0
  Cur LV                1
  Open LV               0
  Max PV                0
  Cur PV                2
  Act PV                2
  VG Size               3.64 TiB
  PE Size               4.00 MiB
  Total PE              953862
  Alloc PE / Size       953862 / 3.64 TiB
  Free  PE / Size       0 / 0   
  VG UUID               9zwhOn-3Qs6-aPTo-kqQ4-RL4p-ICTA-l56Dsz

As you can see, the VG Status has changed to "exported"

Now you can shutdown your system and relocate the drives or reinstall the OS. In my case my OS is installed on a removable Compact Flash card which I have already pre-installed Debian Squeeze. i.e. Here is one I prepared earlier!

OK, once our server has rebooted we need to install LVM and associated utils;

sudo apt-get install lvm2 dmsetup reiserfsprogs xfsprogs

We activate the volume group using the vgchange command again;

vgchange -a y
  Volume group "store" is exported

Import the volume group into our new system with the 'vgimport' command;

vgimport store

Let's have a look at our logical volumes again;

lvdisplay
  --- Logical volume ---
  LV Name                /dev/store/archive
  VG Name                store
  LV UUID                80eFYi-n0Z7-9br1-bbfg-1GQ6-Orxf-0wENTU
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                3.64 TiB
  Current LE             953862
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           254:0

That looks good. It should be the same as it was in the old system and the LV status should be "available"

Take the line from the fstab file on the old server and add it to the new server;

vi /etc/fstab

Paste the line at the end;

UUID=057272e5-8b66-461a-ad18-c1c198c8dcdd /store/archive ext3 errors=remount-ro 0 1

Recreate the mountpoint if it doesn't already exist;

mkdir -p /store/archive

And finally we can mount the drive;

sudo mount /store/archive/

We can check that it is mounted OK with df;

df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1              7387992    930944   6081752  14% /
tmpfs                  1025604         0   1025604   0% /lib/init/rw
udev                   1020856       184   1020672   1% /dev
tmpfs                  1025604         0   1025604   0% /dev/shm
/dev/mapper/store-archive
                     3845710856 2358214040 1292145880  65% /store/archive

And that's it! Glad I didn't need to resort to my backups . . .