Ben's notes

• Restart VM on source host to be sure reboot is successful before the change.

Example migration from iSCSI backed storage host to other host with local LVM based storage.

• List the storage device, here 'vmns2'.

  multipath -ll vmns2
  vmns2 (3600140548f12334da9fed3985da3d6df) dm-14 SYNOLOGY,iSCSI Storage
  size=64G features='0' hwhandler='0' wp=rw
  `-+- policy='round-robin 0' prio=1 status=active
    |- 6:0:0:17 sdo  8:224  active ready running
    `- 7:0:0:17 sdaf 65:240 active ready running

• Shutdown the VM.

  virsh shutdown ns2

• Create compressed image from storage. I used 'pv' to show progress.

  fdisk -l /dev/mapper/vmns2
      Disk /dev/mapper/vmns2: 68.7 GB, 68719476736 bytes
  
  dd if=/dev/mapper/vmns2 bs=1M | pv -s 68719476736 | gzip -c > /var/tmp/ns2-disk-backup.img.gz

• Or use SSH direct:

  dd if=/dev/mapper/vmdesktop bs=1M | pv -s 17179869184 | gzip -c | ssh -c arcfour benst@kvm1 'cat - > /var/tmp/desktop-disk-image.gz'

• Meanwhile… dump the xml.

  virsh dumpxml ns2 > /tmp/ns2.xml

• Copy ns2.xml to new host and import. Edit file to change name / storage device etc…

  virsh define /tmp/ns2.xml

• Create storage, same size as other host.

  lvcreate -L 64G -n vmns2 vg_kvm1

• Copy image to new host, dd image to storage device.

  gunzip -c ns2-disk-backup.img.gz | pv -s 68719476736 | dd of=/dev/vg_kvm1/vmns2 bs=1M
    64GB 0:14:05 [77.5MB/s] [================================>] 100%
  
  134217728+0 records in
  134217728+0 records out
  68719476736 bytes (69 GB) copied, 851.545 s, 80.7 MB/s

• Start vm on new host.

  virsh start vmns2

• Disable autostart on old host.

  virsh autostart --disable ns2

• Enable autostart on new host.

  virsh autostart vmns2

• Clean up vm and storage on old host / NAS.

• Use qemu-img to convert from an lvm to qcow2 format

  qemu-img convert -O qcow2 /dev/vg_name/lv_name/ /var/lib/libvirt/images/image_name.qcow2

• If you want the image compressed add '-c' right after the word convert.
• Edit the xml for the image

  virsh edit image_name

• Modify the disk stanza, adding a type to the driver line; on the source line change 'dev' to 'file' and modify the path:

  driver name='qemu' type='qcow2'
  source file='/var/lib/libvirt/images/image_name.qcow2'

• Shrink the file

  qemu-img convert -c -O qcow2 source.qcow2 shrunk.qcow2