From: John Wilkins Date: Tue, 4 Sep 2012 18:35:33 +0000 (-0700) Subject: doc: Added a new "Data Placement" overview section for added continuity. X-Git-Tag: v0.53~221 X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=3e562001fd3c2db454e02660adeceb51abc6c2ef;p=ceph.git doc: Added a new "Data Placement" overview section for added continuity. Signed-off-by: John Wilkins --- diff --git a/doc/cluster-ops/data-placement.rst b/doc/cluster-ops/data-placement.rst new file mode 100644 index 000000000000..0474ffb94ffa --- /dev/null +++ b/doc/cluster-ops/data-placement.rst @@ -0,0 +1,34 @@ +========================= + 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. + Future versions of Ceph will support namespaces within pools. + +- **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. + +- **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. + +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. If you find some aspects challenging, +`Inktank`_ provides excellent premium support for Ceph. + +.. _Inktank: http://www.inktank.com \ No newline at end of file