Trond Myklebust of Network Appliance, who is also a developer of the Linux Kernel NFS client, told me that the new Linux NFS client behavior is intentional and supported.
Starting with the 2.6.18 Linux kernel, Netapp snapshots have a different device number than the corresponding live volume when viewed with NFS.
The change was made to better support NFS 4, which allows a NFS client to cross mount points on the NFS server provided that the server has exported everything appropriately.
One of the file attributes that a NFS server passes is the FSID (file system ID). On a netapp filer the FSID of a snapshot is different from the FSID of the corresponding live volume. Most NFS clients ignore the FSID attribute.
Steve Losen scl@virginia.edu phone: 434-924-0640
University of Virginia ITC Unix Support