XenMotion is available in all versions of XenServer and allows you to move a running VM from one host to another host, when the VMs disks are located on storage shared by both hosts. This allows for pool maintenance features such as Workload Balancing (WLB), High Availability (HA), and Rolling Pool Upgrade (RPU) to automatically move VMs. These features allow for workload leveling, infrastructure resilience, and the upgrade of server software, without any VM downtime. Storage can only be shared between hosts in the same pool, as a result, VMs can only be moved within the same pool.
Citrix, XenServer/7.3, Enterprise
Live Migration of VMs, VM Mobility, VM Mobility and HA