VMware vMotion Explained: Live VM Migration Without Downtime

vMotion moves the active compute state of a virtual machine from one ESXi host to another while the guest continues running. It supports maintenance and workload balancing by preserving the VM’s network identity and minimizing service interruption.

What moves during a standard migration#

The destination host receives the VM configuration and a progressively synchronized copy of memory while changed pages are tracked. During a brief switchover, execution is transferred to the destination and networking is updated. Virtual disks normally remain on shared storage unless storage migration is also selected.

Core prerequisites#

• Source and destination hosts are managed in a compatible vSphere environment.
• A working VMkernel interface is enabled for vMotion on each host.
• Hosts have reliable, appropriately sized network connectivity for migration traffic.
• The destination can access required datastores or a combined compute-and-storage migration is supported.
• CPU compatibility is satisfied directly or through Enhanced vMotion Compatibility.
• The destination provides compatible port groups, switches, and policy settings.
• The VM has no device or configuration that blocks live migration.

vMotion, Storage vMotion, and combined migration#

Migration phases#

1. vCenter performs compatibility checks.
2. The destination prepares the VM execution context.
3. Memory pages are copied while the source VM continues running.
4. Changed pages are copied in additional passes.
5. The VM pauses briefly and final state is transferred.
6. Execution resumes on the destination and the source state is released.

Network and security considerations#

Use a dedicated or isolated vMotion network, provide redundancy, and protect migration traffic according to the environment’s sensitivity. Encrypted vMotion can protect data in transit on supported configurations. Confirm MTU consistently across the full path before enabling jumbo frames.

Common migration failures#

Operational practice#

Test live migration before a maintenance event, monitor vMotion bandwidth, standardize host networking, keep firmware and supported versions aligned, and verify that backups and monitoring continue after the move. A successful task does not replace application-level health checks.

VMware vSphere documentation