-.IR fsid= num
-This option forces the filesystem identification portion of the file
-handle and file attributes used on the wire to be
-.I num
-instead of a number derived from the major and minor number of the
-block device on which the filesystem is mounted. Any 32 bit number
-can be used, but it must be unique amongst all the exported filesystems.
+.IR fsid= num|root|uuid
+NFS needs to be able to identify each filesystem that it exports.
+Normally it will use a UUID for the filesystem (if the filesystem has
+such a thing) or the device number of the device holding the
+filesystem (if the filesystem is stored on the device).
+
+As not all filesystems are stored on devices, and not all filesystems
+have UUIDs, it is sometimes necessary to explicitly tell NFS how to
+identify a filesystem. This is done with the
+.I fsid=
+option.