doc: Excised content from "Getting Started" and created Intro to Ceph.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>

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+===============
+ Intro to Ceph
+===============
+
+Whether you want to provide :term:`Ceph Object Storage` and/or :term:`Ceph Block
+Device` services to :term:`Cloud Platforms`, deploy a :term:`Ceph Filesystem` or
+use Ceph for another purpose, all :term:`Ceph Storage Cluster` deployments begin
+with setting up each :term:`Ceph Node`, your network and the Ceph Storage
+Cluster. A Ceph Storage Cluster requires at least one Ceph Monitor and at least
+two Ceph OSD Daemons. The Ceph Metadata Server is essential when running Ceph
+Filesystem clients.
+
+.. ditaa::  +---------------+ +---------------+ +---------------+
+            |      OSDs     | |    Monitor    | |      MDS      |
+            +---------------+ +---------------+ +---------------+
+
+- **OSDs**: A :term:`Ceph OSD Daemon` (OSD) stores data, handles data 
+  replication, recovery, backfilling, rebalancing, and provides some monitoring
+  information to Ceph Monitors by checking other Ceph OSD Daemons for a 
+  heartbeat. A Ceph Storage Cluster requires at least two Ceph OSD Daemons to 
+  achieve an ``active + clean`` state when the cluster makes two copies of your
+  data (Ceph makes 2 copies by default, but you can adjust it).
+  
+- **Monitors**: A :term:`Ceph Monitor` maintains maps of the cluster state, 
+  including the monitor map, the OSD map, the Placement Group (PG) map, and the
+  CRUSH map. Ceph maintains a history (called an "epoch") of each state change 
+  in the Ceph Monitors, Ceph OSD Daemons, and PGs.
+
+- **MDSs**: A :term:`Ceph Metadata Server` (MDS) stores metadata on behalf of 
+  the :term:`Ceph Filesystem` (i.e., Ceph Block Devices and Ceph Object Storage
+  do not use MDS). Ceph Metadata Servers make it feasible for POSIX file system 
+  users to execute basic commands like ``ls``, ``find``, etc. without placing 
+  an enormous burden on the Ceph Storage Cluster.
+
+Ceph stores a client's data as objects within storage pools. Using the CRUSH 
+algorithm, Ceph calculates which placement group should contain the object, 
+and further calculates which Ceph OSD Daemon should store the placement group.
+The CRUSH algorithm enables the Ceph Storage Cluster to scale, rebalance, and
+recover dynamically.
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