I dont think i'm entirely sure what your setup looks like. Is the 490GB a VMFS/NFS datastore or a thin provisioned VMDK file attched to a VM?
Generally speaking, vSphere wont see any dedupe savings. They are usually there so you can overprovision at the SAN/Storage Appliance level.
eg within your Windows Storage Server 2012 you can effectively serve 690 GB of data on a 490GB disk.