What is live migration of a virtual machine and how does it work without downtime?

Traditionally, migrating a VM required shutting it down, exporting it, importing it to another host, and restarting it. While functional, this method introduces service interruption. Live migration eliminates that disruption by transferring the VM’s memory state, configuration, and execution context while it is still running .

The process generally follows a pre-copy mechanism. First, a target host creates a shadow VM to receive the source machine’s memory. The system copies memory pages from the source to the destination while the VM continues running. Any memory pages modified during transfer are tracked and resent iteratively. Once the remaining changes are minimal, the source VM is briefly paused, the final memory differences are transferred, storage access is switched to the destination host, and the VM resumes execution there . Network switches are then updated to redirect traffic seamlessly.

Live migration is also useful for load balancing and hardware maintenance. Administrators can shift workloads away from overloaded or aging servers without affecting business operations . However, it may require specific licensing, shared storage, compatible CPUs, and proper network configuration. Cross-platform live migration is typically not supported.