You can safely migrate Cinder volumes between datastores. This enables you to replace datastores, increase resources and capacity, and preserve volumes without taking them offline. The process for migrating volumes depends on several factors. For example, the process is very straightforward if the volume is not attached to an instance. If a volume is attached to an instance, you must migrate the instance.
You cannot migrate any volume that has snapshots attached. You must first detach the snapshots.