From 8e7f2776f2b092882ebe015492929fd36a577898 Mon Sep 17 00:00:00 2001 From: Zac Dover Date: Sat, 22 Apr 2023 10:55:38 +0200 Subject: [PATCH] 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) --- doc/glossary.rst | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/doc/glossary.rst b/doc/glossary.rst index 7aff10bfaf227..b878181944c3d 100644 --- a/doc/glossary.rst +++ b/doc/glossary.rst @@ -309,6 +309,20 @@ 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. -- 2.39.5