How to Perform Safe Cold and Live Migration of KVM VMs Using NFS Shared Storage

Introduction

vm1 runs a KVM virtual machine; vm2 mounts the VM disk via NFS from vm1. After a hot migration on vm1, vm2 shows disk corruption. Using a dedicated NFS storage server avoids the issue.

Prerequisites

All KVM hosts (vm2…vmn) must have the same KVM version installed.

Bridge networking: create a bridge interface and attach eth0 to br0.

Mount paths must be identical on all hosts.

Cold Migration

Disadvantages:

VM must be shut down, causing service interruption (or risk MAC address conflict).

Migration takes longer, especially for large disk images.

Steps:

# scp /etc/libvirt/qemu/qianyi-bridge-vm.xml kafka-2:/etc/libvirt/qemu/qianyi-bridge-vm.xml
# scp /opt/kvm/vm/qianyi-bridge-vm.qcow2 kafka-2:/opt/kvm/vm/qianyi-bridge-vm.qcow2

Define the VM on the destination host: virsh define /tmp/<vm-name>.xml Start the VM:

virsh list --all
virsh start <vm-name>

Test connectivity:

Live Migration

Install NFS on vm3 and ensure all hosts mount the same shared directory.

# virsh migrate --live --verbose domain qemu+ssh://192.168.64.11/system --unsafe
# virsh migrate --live --persistent --undefinesource --verbose myvm qemu+ssh://[email protected]/system --unsafe

Parameter explanations: --live: perform live migration. --verbose: show detailed progress. qemu+ssh://.../system: target host connection via SSH. --unsafe: allow migration without shared storage. --undefinesource: remove VM definition from source after migration. --persistent: keep VM definition on target after host reboot.

Note: Disk paths in both XML files must point to the shared storage directory.

Configure /etc/hosts for name resolution on all hosts.