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migrate-vm: migrate VMs between hosts

Usage

This script is used for migrating KVM virtual machines between physical hosts. The script should be run on the new host for the virtual machine using the following format. The first hostname specified in the command is what physical host to move the virtual machine from, and the second one is the name of the virtual machine to move.

For example, the following command moves supernova from jaws to whatever KVM host the command is run on:

sudo migrate-vm jaws:supernova

Steps performed

To move the virtual machine, migrate-vm performs the following steps:

  1. Shuts down the virtual machine on the old host.
  2. Creates a new LVM volume on the new host with the correct size.
  3. Securely copies the virtual machine's disk from the old host to the new host.
  4. Checksums both the old and the new disks on each machine to ensure they match.
  5. Imports the KVM domain definition from the old host to the new host.

Final steps

After the virtual machine has been transferred between hosts, make sure the guest works on the new host. If moving from hal, you might need to delete the custom CPU definition section from the KVM XML to get the virtual machine to start. To edit the XML definition, run sudo virsh edit ${hostname}. The section to delete looks like this:

<cpu mode='custom' match='exact'>
  <model fallback='allow'>Opteron_G3</model>
</cpu>

Then, after everything works, you should remove the old KVM and LVM definitions on only the old host:

sudo virsh undefine ${hostname}
sudo lvremove /dev/vg/${hostname}

Assumptions Made

  • The LVM volume group /dev/vg is used on both the old and new host.
  • Virtual machines are stored at /dev/vg/${hostname} on both hosts.