No CRUSH involvement in deciding PG target

Quoting from elsewhere "[we calculate] a placement group using the object name, a hash code, the number of PGs in the pool and the pool name"

diff --git a/doc/rados/operations/placement-groups.rst b/doc/rados/operations/placement-groups.rst
index 2d77df6b97bf26bbc95113110a0f1f001264cc67..4fb83bc961677d710f31d2f4d4949ac41fc60851 100644 (file)
--- a/doc/rados/operations/placement-groups.rst
+++ b/doc/rados/operations/placement-groups.rst
@@ -58,11 +58,10 @@ cannot realistically track placement on a per-object basis.
                   |                       |
                   +-----------------------+
 
-Placement groups are invisible to the Ceph user: the CRUSH algorithm
-determines in which placement group the object will be
-placed. Although CRUSH is a deterministic function using the object
-name as a parameter, there is no way to force an object into a given
-placement group.
+The Ceph client will calculate which placement group an object should
+be in. It does this by hashing the object ID and applying an operation
+based on the number of PGs in the defined pool and the ID of the pool.
+See `Mapping PGs to OSDs`_ for details.
 
 The object's contents within a placement group are stored in a set of
 OSDs. For instance, in a replicated pool of size two, each placement