PowerCLI is just awsome 🙂
This simple one-liner migrates all vm’s off one datastore to a new one:
Get-VM -Datastore <datastore1> | Move-VM -Datastore <datastore2>
You can also move vm’s off one datastore and place them in any datastore within a specified datastore cluster:
$DatastoreCluster1 = Get-DatastoreCluster -Name 'DatastoreCluster1' Get-VM -Datastore <datastore1> | Move-VM -Datastore $DatastoreCluster1