Support for VM migration
This section informs what you can expect when migrating virtual machines within a datacenter using vCenter Server migration options. Performance considerations apply to both “hot” and “cold” migration.
VMotion moves a virtual machine’s state and configuration to another host while the machine’s disks remain in the same location on shared storage. VMotion is fully supported for both Agent for ESX/ESXi Virtual Appliance and the virtual machines being backed up by the agent. Migration of either the virtual appliance or a machine can take place during backup.
Storage VMotion moves a virtual machine disks from one datastore to another. Migration of Agent for ESX/ESXi Virtual Appliance with Storage VMotion is possible unless a backup or recovery is in progress. During migration, the agent postpones any backup that has to start. It starts the backup after the migration has been completed.
Migration of a virtual machine with Storage VMotion during backup is possible, but the backup may fail or succeed with warnings. The agent will not be able to delete the snapshot taken before migration because the machine is gone. To avoid this situation, do not migrate a virtual machine until its backup is completed.
It is critical to understand that backup performance degrades when Agent for ESX/ESXi does not have direct access to the storage where the backed up disks are. In this case, the agent cannot attach the disks. Instead, it obtains data from these disks through LAN. This process is much slower than obtaining data from directly attached disks.
So the best practice is that Agent for ESX/ESXi Virtual Appliance be hosted on a host for which all shared storages of the cluster are accessible. In this case, backup performance remains optimal, wherever (within the shared storages) a virtual machine or the virtual appliance migrates. Once a machine migrates to a local storage of a different host, its backups will run slower.