Gate zfs grain on Windows

salt/grains/zfs.py

@@ -45,6 +45,9 @@ def __virtual__():
     '''
     # NOTE: we always load this grain so we can properly export
     #       at least the zfs_support grain
+    #       except for Windows... don't try to load this on Windows (#51703)
+    if salt.utils.platform.is_windows():
+        return False, 'ZFS: Not available on Windows'
     return __virtualname__