doc/cephadm: Co-location of daemons

Signed-off-by: Sebastian Wagner <sewagner@redhat.com>

doc/cephadm/services/index.rst

@@ -402,6 +402,30 @@ YAML can also be used to specify limits on hosts:
         - host2
         - host3
 
+.. _cephadm_co_location:
+
+Co-location of daemons
+----------------------
+
+Cephadm supports the deployment of multiple daemons on the same host:
+
+.. code-block:: yaml
+
+    service_type: rgw
+    placement:
+      label: rgw
+      count-per-host: 2
+
+The main reason for deploying multiple daemons per host is an additional
+performance benefit for running multiple RGW and MDS daemons on the same host.
+
+See also: 
+
+* :ref:`cephadm_mgr_co_location`.
+* :ref:`cephadm-rgw-designated_gateways`.
+
+This feature was introduced in Pacific.
+
 Algorithm description
 ---------------------
 

doc/cephadm/services/mgr.rst

@@ -22,13 +22,19 @@ example spec file (leveraging a default placement):
     networks:
     - 192.169.142.0/24
 
+.. _cephadm_mgr_co_location:
+
 Allow co-location of MGR daemons
 ================================
 
 In deployment scenarios with just a single host, cephadm still needs
-to deploy at least two MGR daemons. See ``mgr_standby_modules`` in
+to deploy at least two MGR daemons in order to allow an automated
+upgrade of the cluster. See ``mgr_standby_modules`` in
 the :ref:`mgr-administrator-guide` for further details.
 
+See also: :ref:`cephadm_co_location`.
+
+
 Further Reading
 ===============
 

doc/cephadm/services/rgw.rst

@@ -36,6 +36,8 @@ under the arbitrary service id *foo*:
 
    ceph orch apply rgw foo
 
+.. _cephadm-rgw-designated_gateways:
+
 Designated gateways
 -------------------
 
@@ -49,6 +51,8 @@ ports 8000 and 8001:
    ceph orch host label add gwhost2 rgw
    ceph orch apply rgw foo '--placement=label:rgw count-per-host:2' --port=8000
 
+See also: :ref:`cephadm_co_location`.
+
 .. _cephadm-rgw-networks:
 
 Specifying Networks