Following NFS mount parameters are required for XEN:
CLI mount: "-o tcp,hard,int"
XEN GUI: "tcp,hard,int" [-o should be discarded]
tcp option informs system to use TCP protocol.
hard mount is generally used for block resources like a local disk or SAN.
intr If hard is specified, the user cannot terminate the process waiting for the NFS communication to resume unless the intr option is also specified. intr allows NFS requests to be interrupted if the server goes down or cannot be reached.