Add more details to the description of the fsid_guid dataset property
6333 ZFS should let the user specify or modify the fsid_guid of a dataset

@@ -1059,10 +1059,18 @@
 .Sy filesystem_limit ,
 but rather imposes an additional limit. This feature must be enabled to be used
 .Po see
 .Xr zpool-features 5
 .Pc .
+.It Sy fsid_guid Ns = Ns Sy value Ns
+Sets the dataset fsid_guid. The fsid_guid is a 64-bit unsigned integer, used to
+construct the vfs id when mounting a dataset.
+This property should only be set if you need the vfs id to be identical on two
+systems, for example in a NFS migration scenario.
+When the fsid_guid is changed for a file system, the file system and any
+children that inherit the mountpoint are unmounted, then remounted. If the
+file system was shared, existing NFS clients will require a remount.
 .It Sy mountpoint Ns = Ns Pa path Ns | Ns Sy none Ns | Ns Sy legacy
 Controls the mount point used for this file system. See the
 .Sx Mount Points
 section for more information on how this property is used.
 .Pp