From: Zac Dover Date: Sat, 22 Apr 2023 08:55:38 +0000 (+0200) Subject: doc/glossary: add "Placement Groups" definition X-Git-Tag: v18.1.0~167^2 X-Git-Url: http://git.apps.os.sepia.ceph.com/?a=commitdiff_plain;h=9e041b870df17e633850170d1337452dabbb11c6;p=ceph-ci.git doc/glossary: add "Placement Groups" definition Add a definition of "Placement Groups" to the Glossary. Co-authored-by: Anthony D'Atri Signed-off-by: Zac Dover (cherry picked from commit 9f37ea651f9ee2c51e0705b9b58ed356f1bc56e6) --- diff --git a/doc/glossary.rst b/doc/glossary.rst index ea72ae8c268..9f685e42c7f 100644 --- a/doc/glossary.rst +++ b/doc/glossary.rst @@ -311,6 +311,20 @@ state of a multi-site configuration. When the period is updated, the "epoch" is said thereby to have been changed. + Placement Groups (PGs) + Placement groups (PGs) are subsets of each logical Ceph pool. + Placement groups perform the function of placing objects (as a + group) into OSDs. Ceph manages data internally at + placement-group granularity: this scales better than would + managing individual (and therefore more numerous) RADOS + objects. A cluster that has a larger number of placement groups + (for example, 100 per OSD) is better balanced than an otherwise + identical cluster with a smaller number of placement groups. + + Ceph's internal RADOS objects are each mapped to a specific + placement group, and each placement group belongs to exactly + one Ceph pool. + :ref:`Pool` A pool is a logical partition used to store objects.