Merge pull request #11193 from nextcloud/backport/11190/stable27

[stable27] Update auth_mechanisms.rst

admin_manual/configuration_files/external_storage/auth_mechanisms.rst

@@ -59,6 +59,8 @@ The **Global credentials** mechanism uses the general input field for "Global
 credentials" in the external storage settings section as source for the
 credentials instead of individual credentials for a mount point.
 
+:ref:`Considerations for shared storage <considerations_for_shared_storage_label>`
+
 Public-key mechanisms
 ---------------------
 
@@ -74,3 +76,16 @@ See :doc:`./sftp` for additional information on how to set up certificate based
 
 .. figure:: images/auth_rsa.png
    :alt: Form on admin page for generating RSA keys.
+
+.. _considerations_for_shared_storage_label:
+
+Considerations for shared storage
+---------------------------------
+
+Every external storage, which is using user specific authentication, is connected individually.
+Even if several users connect to the same folder, the files are regarded as separate files per user.
+Nextcloud can not recognize if two users access the very same file if they follow individual connections. 
+
+This has an influence on e.g. file locking as a locked individual file is not shown as locked to other users or users cannot collaboratively edit documents.
+
+If collaborative working on external storage is required, the authentication "Global credentials" has to be used.