mirror of
https://github.com/ceph/ceph
synced 2024-12-23 03:44:23 +00:00
38 lines
1.9 KiB
ReStructuredText
38 lines
1.9 KiB
ReStructuredText
=========================
|
|
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
|