NFS V4 clients can back up NFS file systems that are mounted by using the global namespace feature, which is called a referral. All file systems in the global namespace are backed up under a single file space.
server 'publications' has /doc file system
server 'projects' has /projects file system
server 'data' has /data file system
/doc -vers=4,refer=/doc@publications
/projects -vers=4,refer=/projects@projects
/data -vers=4,refer=/data@data
payroll:/#mount -o vers=4 account1:/ /mnt
payroll:/#ls /mnt
doc/ projects/ data/
The client payroll can back up the /mnt file as one NFS file system, which backs up all other file systems.
VIRTUALMOUNTPOINT /doc
VIRTUALMOUNTPOINT /projects
VIRTUALMOUNTPOINT /data