Adding upstream version 14.2.21.upstream/14.2.21upstream

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

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+=========================
+ Data Placement Overview
+=========================
+
+Ceph stores, replicates and rebalances data objects across a RADOS cluster
+dynamically.  With many different users storing objects in different pools for
+different purposes on countless OSDs, Ceph operations require some data
+placement planning.  The main data placement planning concepts in Ceph include:
+
+- **Pools:** Ceph stores data within pools, which are logical groups for storing
+  objects. Pools manage the number of placement groups, the number of replicas,
+  and the CRUSH rule for the pool. To store data in a pool, you must have
+  an authenticated user with permissions for the pool. Ceph can snapshot pools.
+  See `Pools`_ for additional details.
+
+- **Placement Groups:** Ceph maps objects to placement groups (PGs).
+  Placement groups (PGs) are shards or fragments of a logical object pool
+  that place objects as a group into OSDs. Placement groups reduce the amount
+  of per-object metadata when Ceph stores the data in OSDs. A larger number of
+  placement groups (e.g., 100 per OSD) leads to better balancing. See
+  `Placement Groups`_ for additional details.
+
+- **CRUSH Maps:**  CRUSH is a big part of what allows Ceph to scale without
+  performance bottlenecks, without limitations to scalability, and without a
+  single point of failure. CRUSH maps provide the physical topology of the
+  cluster to the CRUSH algorithm to determine where the data for an object
+  and its replicas should be stored, and how to do so across failure domains
+  for added data safety among other things. See `CRUSH Maps`_ for additional
+  details.
+
+- **Balancer:** The balancer is a feature that will automatically optimize the
+  distribution of PGs across devices to achieve a balanced data distribution,
+  maximizing the amount of data that can be stored in the cluster and evenly
+  distributing the workload across OSDs.
+
+When you initially set up a test cluster, you can use the default values. Once
+you begin planning for a large Ceph cluster, refer to pools, placement groups
+and CRUSH for data placement operations.
+
+.. _Pools: ../pools
+.. _Placement Groups: ../placement-groups
+.. _CRUSH Maps: ../crush-map
+.. _Balancer: ../balancer