diff --git a/docs/administration-guide.rst b/docs/administration-guide.rst
index 0637df2d..1d9232d8 100644
--- a/docs/administration-guide.rst
+++ b/docs/administration-guide.rst
@@ -139,6 +139,12 @@ or ``zfs``) to store the backup data.
 Datastores are identified by a simple *ID*. You can configure it
 when setting up the backup server.
 
+.. note:: The `File Layout`_ requires the file system to support more than
+   65537 subdirectories per directory. This excludes certain filesystems and
+   filesystem configuration from being supported as datastore. For example
+   ``ext4`` without the ``dir_nlink`` feature (which is enabled by default)
+   and ``ext3``.
+
 
 
 Datastore Configuration