On one vCenter Server, the moRef uniquely identifies a virtual machine. If you need to track and inventory virtual machine backups across multiple vCenter Servers, you can use moRef together with instanceUuid. You can see the instanceUuid at the following browser path:


For direct connections to ESXi, the host address and moRef uniquely identify a virtual machine. However this moRef could be different from the one that vCenter Server returns, hence the fallback to instanceUuid. The instanceUuid was new in VMware vSphere 4.0. In previous releases, the fallback was to Uuid.