View source for Network/Procedures/Convert a normal logical volume to a DRBD

Adapted from [http://lists.linbit.com/pipermail/drbd-user/2009-February/011464.html]. This is useful for migrating from an LVM-based VM host to a more robust DRBD-on-LVM setup.

Start on the source box.
* <code>lvextend -L +128m kratos/backup</code> (where "kratos" is the volume group and "backup" is the volume name)
* Create /etc/drbd.d/backup_disk.res (for example) and make it look like this:
<code> 
 resource backup_disk {
        protocol C;
        meta-disk internal;
        device /dev/drbd_backup_disk minor 7; #dev and minor must be unique per disk
        syncer {
                verify-alg sha1;
                rate 5M;
        }
        net {
                allow-two-primaries;# yes;
                cram-hmac-alg sha1;
                shared-secret "backup_disk";
        }
        on kratos {
                disk /dev/kratos/backup;
                address 10.56.0.2:7795; #port must be unique per disk
        }
        on vm2 {
                disk /dev/vm2_storage/backup_disk;
                address 10.56.0.20:7795;
        }
 } 
</code>
Then, scp this file to the other box's /etc/drbd.d/ directory, too.
* <code>fdisk -l /dev/kratos/backup | head -n 2</code> and make a note of the size, in bytes, of the volume.
* <code>drbdadm create-md backup_disk</code> (it'll tell you it might nuke something by writing metadata, but we extended the volume 128MB to accommodate this, so accept that)
* At this point you are going to want to bring down your VM and point it to /dev/drbd_backup_disk (or whatever) instead of its old disk. Don't start it though.
* <code>drbdadm attach backup_disk</code>
* <code>drbdadm -- --overwrite-data-of-peer primary backup_disk</code> (Force this machine to come up as the "gold copy" of the data, and clobber the secondary we will attach later)
* <code>cat /proc/drbd</code> (your volume status will be Primary/Unknown)
* At this point you can boot the VM again.

Now, on the replication target (new box):
* <code>lvcreate --name backup_disk --size 74222403584B vm2_storage</code> (where "backup_disk" is the name of your logical volume, "74222403584B" is the size from when you ran <code>fdisk -l</code> earlier, and "vm2_storage" is the volume group)
* <code>drbdadm create-md backup_disk</code> (you shouldn't have to confirm anything if this is a blank disk)
* <code>drbdadm adjust backup_disk</code> (The connection won't happen just yet)

Now, finally, back on your primary box: 
* <code>drbdadm adjust backup_disk</code>

Now you can <code>watch cat /proc/drbd</code> on either box and you should watch your volume synch!