doc/start: Add Beginner's Guide

Add a Beginner's Guide to docs.ceph.com.

Signed-off-by: Zac Dover <zac.dover@proton.me>
(cherry picked from commit 91aafc6a7f72c105fbf3aa8419863e931d5b9e00)

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+==========================
+ Beginner's Guide
+==========================
+
+The purpose of A Beginner's Guide to Ceph is to make Ceph comprehensible.
+
+Ceph is a clustered and distributed storage manager. If that's too cryptic,
+then just think of Ceph as a computer program that stores data and uses a
+network to make sure that there is a backup copy of the data.
+
+Ceph offers several "storage interfaces", which is another
+way of saying "ways of storing data". These storage interfaces include: 
+- CephFS (a file system) 
+- RBD (block devices) 
+- RADOS (an object store).
+
+Deep down, though, all three of these are really RADOS object stores. CephFS
+and RBD are just presenting themselves as file systems and block devices.
+
+Ceph is a clustered and distributed storage manager that offers data
+redundancy. This sentence might be too cryptic for first-time readers of the
+Ceph Beginner's Guide, so let's explain all of the terms in it:
+
+- **Storage Manager.** Ceph is a storage manager. This means that Ceph is
+  software that helps storage resources store data. Storage resources come in
+  several forms: hard disk drives (HDD), solid-state drives (SSD), magnetic
+  tape, floppy disks, punched tape, Hoellerith-style punch cards, and magnetic
+  drum memory are all forms of storage resources. In this beginner's guide,
+  we'll focus on hard disk drives (HDD) and solid-state drives (SSD).
+- **Clustered storage manager** Ceph is a clustered storage manager. That means
+  that the storage manager installed not just on a single machine but on
+  several machines that work together as a system.
+- **Distributed storage manager.** Ceph is a clustered and distributed storage
+  manager. That means that the data that is stored and the infrastructure that
+  supports it is spread across multiple machines and is not centralized in a
+  single machine. To better understand what distributed means in this context,
+  it might be helpful to describe what it is not: it is not a system ISCSI,
+  which is a system that exposes a single logical disk over the network in a
+  1:1 (one-to-one) mapping.
+- **Data Redundancy.** Having a second copy of your data somewhere.
+
+Ceph Monitor 
+------------
+
+The Ceph Monitor is one of the daemons essential to the functioning of a Ceph
+cluster. Monitors know the location of all the data in the Ceph cluster.
+Monitors maintain maps of the cluster state, and those maps make it possible
+for Ceph daemons to work together. These maps include the monitor map, the OSD
+map, the MDS map, and the CRUSH map. Three monitors are required to reach
+quorum. Quorum is a state that is necessary for a Ceph cluster to work
+properly. Quorum means that a majority of the monitors are in the "up" state.
+
+MANAGER
+-------
+The manager balances the data in the Ceph cluster, distributing load evenly so
+that no part of the cluster gets overloaded. The manager is one of the daemons
+essential to the functioning of the Ceph cluster. Managers keep track of
+runtime metrics, system utilization, CPU performance, disk load, and they host
+the Ceph dashboard web GUI.
+
+OSD
+---
+
+Object Storage Daemons (OSDs) store objects.
+
+An OSD is a process that runs on a storage server. The OSD is responsible for
+managing a single unit of storage, which is usually a single disk.
+
+POOLS
+-----
+
+A pool is an abstraction that can be designated as either "replicated" or
+"erasure coded". In Ceph, the method of data protection is set at the pool
+level. Ceph offers and supports two types of data protection: replication and
+erasure coding. Objects are stored in pools. "A storage pool is a collection of
+storage volumes. A storage volume is the basic unit of storage, such as
+allocated space on a disk or a single tape cartridge. The server uses the
+storage volumes to store backed-up, archived, or space-managed files." (IBM
+Tivoli Storage Manager, Version 7.1, "Storage Pools")
+
+PLACEMENT GROUPS
+----------------
+
+Placement groups are a part of pools.
+
+MDS
+---
+A metadata server (MDS) is necessary for the proper functioning of CephFS.
+See :ref:`orchestrator-cli-cephfs` and :ref:`arch-cephfs`.
+
+
+

diff --git a/doc/start/intro.rst b/doc/start/intro.rst
index 390f1b2d8d52dc8ed7dedf998670c5acc5f87490..1cbead4a3df0b3038256793879e304cb4fad14ae 100644 (file)
--- a/doc/start/intro.rst
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@@ -78,6 +78,7 @@ recover dynamically.
       .. toctree::
          :maxdepth: 2
 
+         Beginner's Guide <beginners-guide>
          Hardware Recommendations <hardware-recommendations>
          OS Recommendations <os-recommendations>