BTW. You should configure the LUNs for thin provisioning and dedupe, this should help.
http://blogs.netapp.com/drdedupe/2010/05/netapp-luns-and-deduplication.htmlKeep in mind that because the VMs are on a LUN vs NFS mount you will not see the space savings on the datastore and will keep a track of the space on the Netapp.
My $.02