DOCS-972 sync from hidden members

source/core/read-preference.txt

@@ -525,6 +525,8 @@ using non-:readmode:`primary` read preference modes:
   direct connection to a :ref:`hidden member
   <replica-set-hidden-members>` of the set.
 
+  .. include:: /includes/fact-replica-set-sync-prefers-non-hidden.rst
+
 - Providing local reads for geographically distributed applications.
 
   If you have application servers in multiple data centers, you may

source/core/replica-set-architectures.txt

@@ -141,6 +141,8 @@ more of the following categories:
   from such outputs prevents clients and drivers from using hidden
   members for secondary reads. (See: :ref:`replica-set-hidden-members`.)
 
+  .. include:: /includes/fact-replica-set-sync-prefers-non-hidden.rst
+
 - **Voting**: This changes the number of votes that a member of the
   replica set has in elections. In general, use priority to control the
   outcome of elections, as weighting votes introduces operational
@@ -242,7 +244,7 @@ primary *and* a quorum of voting members in the main facility.
    these members, so that they won't vote in elections.
 
 .. seealso:: :ref:`Secondary Only <replica-set-secondary-only-members>`,
-   and :ref:`Hidden Nodes <replica-set-hidden-members>`.
+   and :ref:`Hidden Members <replica-set-hidden-members>`.
 
 .. _replica-set-arbiter-nodes:
 

source/core/replication-internals.txt

@@ -257,6 +257,8 @@ entries from other members. Members sync data at two different points:
 - *Replication* occurs continually after initial sync and keeps the
   member updated with changes to the replica set's data.
 
+  .. include:: /includes/fact-replica-set-sync-prefers-non-hidden.rst
+
 In MongoDB 2.0, secondaries only change sync targets if the connection
 to the sync target drops [#connection-drop]_ or produces an error.
 

source/includes/fact-replica-set-sync-prefers-non-hidden.rst

@@ -0,0 +1,10 @@
+If :data:`~local.system.replset.settings.chainingAllowed` is enabled,
+allowing secondary members to sync from other secondaries, MongoDB will
+by default choose non-hidden members over hidden members and will only
+choose hidden members as a last resort. In cases where you want a
+secondary to sync from a hidden member first, use the
+:dbcommand:`replSetSyncFrom` database command. The command has several
+caveats. Refer to the documentation for :dbcommand:`replSetSyncFrom`
+before using the command.
+
+.. seealso:: :doc:`/tutorial/manage-chained-replication`

source/tutorial/configure-a-hidden-replica-set-member.txt

@@ -14,6 +14,8 @@ from normal traffic. Typically, hidden members provide reporting,
 dedicated backups, and dedicated read-only testing and integration
 support.
 
+.. include:: /includes/fact-replica-set-sync-prefers-non-hidden.rst
+
 Hidden members have :data:`~local.system.replset.members[n].priority` set
 ``0`` and have :data:`~local.system.replset.members[n].hidden` set to ``true``.