Adding upstream version 18.2.2.upstream/18.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. _cephfs-multifs:
+
+Multiple Ceph File Systems
+==========================
+
+
+Beginning with the Pacific release, multiple file system support is stable
+and ready to use. This functionality allows configuring separate file systems
+with full data separation on separate pools.
+
+Existing clusters must set a flag to enable multiple file systems::
+
+    ceph fs flag set enable_multiple true
+
+New Ceph clusters automatically set this.
+
+
+Creating a new Ceph File System
+-------------------------------
+
+The new ``volumes`` plugin interface (see: :doc:`/cephfs/fs-volumes`) automates
+most of the work of configuring a new file system. The "volume" concept is
+simply a new file system. This can be done via::
+
+    ceph fs volume create <fs_name>
+
+Ceph will create the new pools and automate the deployment of new MDS to
+support the new file system. The deployment technology used, e.g. cephadm, will
+also configure the MDS affinity (see: :ref:`mds-join-fs`) of new MDS daemons to
+operate the new file system.
+
+
+Securing access
+---------------
+
+The ``fs authorize`` command allows configuring the client's access to a
+particular file system. See also in :ref:`fs-authorize-multifs`. The client will
+only have visibility of authorized file systems and the Monitors/MDS will
+reject access to clients without authorization.
+
+
+Other Notes
+-----------
+
+Multiple file systems do not share pools. This is particularly important for
+snapshots but also because no measures are in place to prevent duplicate
+inodes. The Ceph commands prevent this dangerous configuration.
+
+Each file system has its own set of MDS ranks. Consequently, each new file
+system requires more MDS daemons to operate and increases operational costs.
+This can be useful for increasing metadata throughput by application or user
+base but also adds cost to the creation of a file system. Generally, a single
+file system with subtree pinning is a better choice for isolating load between
+applications.