From 08a342485c9ffc957e959ad3f5d4abc3b092bfb0 Mon Sep 17 00:00:00 2001 From: Patrick Donnelly Date: Tue, 12 Dec 2023 11:45:05 -0500 Subject: [PATCH] doc/cephfs: add docs for balance_automate Signed-off-by: Patrick Donnelly --- doc/cephfs/multimds.rst | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/doc/cephfs/multimds.rst b/doc/cephfs/multimds.rst index 02564db45a889..d105c74ad62cb 100644 --- a/doc/cephfs/multimds.rst +++ b/doc/cephfs/multimds.rst @@ -243,6 +243,31 @@ value to `-1`. $ setfattr -n ceph.dir.pin -v -1 home +Dynamic Subtree Partitioning +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +CephFS has long had a dynamic metadata blanacer (sometimes called the "default +balancer") which can split or merge subtrees while placing them on "colder" MDS +ranks. Moving the metadata around can improve overall file system throughput +and cache size. + +However, the balancer has suffered from problem with efficiency and performance +so it is by default turned off. This is to avoid an administrator "turning on +multimds" by increasing the ``max_mds`` setting and then finding the balancer +has made a mess of the cluster performance (reverting is straightforward but +can take time). + +The setting to turn on the balancer is: + +.. prompt:: bash # + + ceph fs set balance_automate true + +Turning on the balancer should only be done with appropriate configuration, +such as with the ``bal_rank_mask`` setting (described below). Careful +monitoring of the file system performance and MDS is advised. + + Dynamic subtree partitioning with Balancer on specific ranks ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- 2.39.5