doc: do not encourage readers to run multiple clusters on same HW

doc/rados/configuration/common.rst

@@ -183,76 +183,20 @@ Example ceph.conf
 
 
 
-Running Multiple Clusters
-=========================
+Running Multiple Clusters (DEPRECATED)
+======================================
 
-With Ceph, you can run multiple Ceph Storage Clusters on the same hardware.
-Running multiple clusters provides a higher level of isolation compared to
-using different pools on the same cluster with different CRUSH rules. A
-separate cluster will have separate monitor, OSD and metadata server processes.
-When running Ceph with default settings, the default cluster name is ``ceph``,
-which means you would save your Ceph configuration file with the file name
-``ceph.conf`` in the ``/etc/ceph`` default directory.
+Some Ceph CLI commands take a ``-c`` (cluster name) option. This option is
+present purely for backward compatibility. You should not attempt to deploy
+or run multiple clusters on the same hardware, and it is recommended to always
+leave the cluster name as the default ("ceph").
 
-See `Create a Cluster`_ for details.
-
-.. _Create a Cluster: ../../deployment/ceph-deploy-new
-
-When you run multiple clusters, you must name your cluster and save the Ceph
-configuration file with the name of the cluster. For example, a cluster named
-``openstack`` will have a Ceph configuration file with the file name
-``openstack.conf`` in the  ``/etc/ceph`` default directory.
-
-.. important:: Cluster names must consist of letters a-z and digits 0-9 only.
-
-Separate clusters imply separate data disks and journals, which are not shared
-between clusters. Referring to `Metavariables`_, the ``$cluster``  metavariable
-evaluates to the cluster name (i.e., ``openstack`` in the  foregoing example).
-Various settings use the ``$cluster`` metavariable, including:
-
-.. _Metavariables: ../ceph-conf#Metavariables
-
-- ``keyring``
-- ``admin socket``
-- ``log file``
-- ``pid file``
-- ``mon data``
-- ``mon cluster log file``
-- ``osd data``
-- ``osd journal``
-- ``mds data``
-- ``rgw data``
-
-See `General Settings`_, `OSD Settings`_, `Monitor Settings`_, `MDS Settings`_,
-`RGW Settings`_ and `Log Settings`_ for relevant path defaults that use the
-``$cluster`` metavariable.
-
-.. _General Settings: ../general-config-ref
-.. _OSD Settings: ../osd-config-ref
-.. _Monitor Settings: ../mon-config-ref
-.. _MDS Settings: ../../../cephfs/mds-config-ref
-.. _RGW Settings: ../../../radosgw/config-ref/
-.. _Log Settings: ../../troubleshooting/log-and-debug
-
-
-When creating default directories or files, you should use the cluster
-name at the appropriate places in the path. For example::
-
-	sudo mkdir /var/lib/ceph/osd/openstack-0
-	sudo mkdir /var/lib/ceph/mon/openstack-a
-
-.. important:: When running monitors on the same host, you should use
-   different ports. By default, monitors use port 6789. If you already
-   have monitors using port 6789, use a different port for your other cluster(s).
-
-To invoke a cluster other than the default ``ceph`` cluster, use the
-``-c {filename}.conf`` option with the ``ceph`` command. For example::
-
-	ceph -c {cluster-name}.conf health
-	ceph -c openstack.conf health
+If you need to allow multiple clusters to exist on the same host, please use
+`cephadm`_, which uses containers to fully isolate each cluster.
 
 
 .. _Hardware Recommendations: ../../../start/hardware-recommendations
 .. _Network Configuration Reference: ../network-config-ref
 .. _OSD Config Reference: ../osd-config-ref
 .. _Configuring Monitor/OSD Interaction: ../mon-osd-interaction
+.. _cephadm: ../../cephadm