docs: Add instructions for Ceph shutdown

Author: Alex-Welsh

doc/source/operations/control-plane-operation.rst

@@ -175,7 +175,29 @@ Ceph
 ----
 
 The following guide provides a good overview:
-https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/8/html/director_installation_and_usage/sect-rebooting-ceph
+`<https://www.croit.io/blog/how-not-to-shut-down-a-ceph-cluster>`_.
+
+#. Check that the cluster is healthy (i.e. ``ceph -s``). Where possible, solve
+   or isolate any issues before the shutdown e.g. by marking unhealthy OSDs as
+   'out' in the cluster.
+
+#. Stop all clients. This includes
+
+   * **All** OpenStack VMs (if their storage is RBD basted).
+
+   * CephFS mounts.
+
+   * Ceph-backed openstack services such as Glance, Cinder, and RGW/S3/Swift.
+
+#. Set the ``noout`` flag, so that the cluster does not attempt to redistribute
+   the data by creating extra copies or EC shards elsewhere when the OSDs go
+   down.
+
+#. Shut down all the nodes, with those holding MON services last.
+
+Note that if it is not desired for Ceph services to automatically start later
+with the operating system, extra steps need to be taken and are not described
+here.
 
 Shutting down the seed VM
 -------------------------