Transferring to/from NAS (i.e. NFS v3 TCP, NFS over UDP and CIFS is \*NOT* supported and does not work) can be very slow, but once it's up and working, performance is reasonable for a few low utilization VM's. I store all of my ISO files and Templates on an NFS datastore housed on a NetApp filer for various reasons, and when I run updates to them, for the most part, things run at a reasonable pace. However, deploying from template is obviously slower than using a SAN (FC or iSCSI) based source.