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diff --git a/src/ceph/doc/rados/operations/data-placement.rst b/src/ceph/doc/rados/operations/data-placement.rst new file mode 100644 index 0000000..27966b0 --- /dev/null +++ b/src/ceph/doc/rados/operations/data-placement.rst @@ -0,0 +1,37 @@ +========================= + 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 ruleset 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. + +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 |