Manually migrate LVM based vm from one KVM hosts to another

Posted On July 13, 2016

We have a KVM based VM on LVM volume that we need to migrate to different host. This is not hot-live migration and will be done offline. Lets looks at steps required to get it done. There may be many different ways to do it and this is just one of them.

Both of our KVM hosts configured exactly the same. Both have volume group vm-images that hold virtual machines LVM’s

ServerA#vgdisplay

--- Volume group ---
  VG Name               vm-images
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  55
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               2
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               931.51 GiB
  PE Size               4.00 MiB
  Total PE              238466
  Alloc PE / Size       5000 / 19.53 GiB
  Free  PE / Size       233466 / 911.98 GiB
  VG UUID               F8BExR-ZUTy-JzoV-HKEC-xxxx-y3ze-g4dpxp

Lest assume serverA and serverB and we need to migrate vm called DC from serverA to serverB

Step 1

Run lvdisplay on serverA to determine size of LVM used by our vm called DC

serverA#lvdisplay
--- Logical volume ---
  LV Path                /dev/vm-images/DC
  LV Name                DC
  VG Name                vm-images
  LV UUID                eUYUQ0-6KF9-XXXX-4b8z-DdIb-7vLQ-8m7HTg
  LV Write Access        read/write
  LV Creation host, time serverA, 2016-06-08 09:26:50 -0400
  LV Status              available
  # open                 0
  LV Size                39.06 GiB
  Current LE             10000
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:2

Step 2

Note the size of LV volume from step 1 (in our case 40G) and create LVM on serverB with exactly same size and name using same Volume Group as the one on serverA (VG and name does not have to be the same. In our case it is for consistency)

serverB#lvcreate -L 40G -n DC vm-images
 Logical volume "DC" created.

Step 3

Shutdown your VM on serverA from VM or bu using virsh

virsh destroy DC

Step 4

Use dd with ssh to transfer Volume over to serverB. To monitor progress you can install pv

yum install pv

dd if=/dev/vm-images/DC | pv | ssh root@serverB 'dd of=/dev/vm-images/DC'

Step 5

Dump the xml definition on serverA. Run virsh list –all to find name of your vm

virsh dumpxml DC > DC.xml

Step 6

Transfer DC.xml from serverA to ServerB

serverA# scp DC.xml root@serverB:/root

Step 7

Define new vm on serverB

serverB#virsh define DC.xml

Step 8

Start new vm

serverB#virsh start DC