mgr/dashboard: update dashboard docs with RBD image monitoring paragraph

Signed-off-by: Patrick Seidensal <pseidensal@suse.com>
(cherry picked from commit 0c0e6ee496520145782d82a250c0d0f59378222f)

Conflicts:
	doc/mgr/dashboard.rst
	Fixed conflict because https://github.com/ceph/ceph/commit/d6369ac159a759b00769c0af34131ecba422e8d5
	has not been backported to octopus.

diff --git a/doc/mgr/dashboard.rst b/doc/mgr/dashboard.rst
index be298a5696eea2d643e4cc9bca97f3c705616ee4..216f9516c7b326adde2f681456398a3b2c618344 100644 (file)
--- a/doc/mgr/dashboard.rst
+++ b/doc/mgr/dashboard.rst
@@ -468,6 +468,14 @@ More details can be found in the documentation of the :ref:`mgr-prometheus`.
     [security]
     allow_embedding = true
 
+Enabling RBD-Image monitoring
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Due to performance reasons, monitoring of RBD images is disabled by default. For
+more information please see :ref:`prometheus-rbd-io-statistics`. If disabled,
+the overview and details dashboards will stay empty in Grafana and the metrics
+will not be visible in Prometheus.
+
 After you have set up Grafana and Prometheus, you will need to configure the
 connection information that the Ceph Dashboard will use to access Grafana.