From dcb340f3d82984055f488501cbfe4c267be4f98a Mon Sep 17 00:00:00 2001 From: Patrick Donnelly Date: Wed, 21 Apr 2021 20:41:43 -0700 Subject: [PATCH] doc: clarify distributed ephemeral pins new mechanism This documentation was for the old code, the new code (by Zheng) fragments the directory and distributes those fragments. Fixes: https://tracker.ceph.com/issues/51187 Signed-off-by: Patrick Donnelly --- doc/cephfs/multimds.rst | 25 ++++++------------------- 1 file changed, 6 insertions(+), 19 deletions(-) diff --git a/doc/cephfs/multimds.rst b/doc/cephfs/multimds.rst index c257285072d03..5c9df8865e5ac 100644 --- a/doc/cephfs/multimds.rst +++ b/doc/cephfs/multimds.rst @@ -164,10 +164,12 @@ your metadata throughput with no other administrative intervention. Presently, there are two types of ephemeral pinning: -**Distributed Ephemeral Pins**: This policy indicates that **all** of a -directory's immediate children should be ephemerally pinned. The canonical -example would be the ``/home`` directory: we want every user's home directory -to be spread across the entire MDS cluster. This can be set via: +**Distributed Ephemeral Pins**: This policy causes a directory to fragment +(even well below the normal fragmentation thresholds) and distribute its +fragments as ephemerally pinned subtrees. This has the effect of distributing +immediate children across a range of MDS ranks. The canonical example use-case +would be the ``/home`` directory: we want every user's home directory to be +spread across the entire MDS cluster. This can be set via: :: @@ -221,18 +223,3 @@ For the reverse situation: The ``home/patrick`` directory and its children will be pinned to rank 2 because its export pin overrides the policy on ``home``. - -If a directory has an export pin and an ephemeral pin policy, the export pin -applies to the directory itself and the policy to its children. So: - -:: - - mkdir -p home/{patrick,john} - setfattr -n ceph.dir.pin -v 0 home - setfattr -n ceph.dir.pin.distributed -v 1 home - -The home directory inode (and all of its directory fragments) will always be -located on rank 0. All children including ``home/patrick`` and ``home/john`` -will be ephemerally pinned according to the distributed policy. This may only -matter for some obscure performance advantages. All the same, it's mentioned -here so the override policy is clear. -- 2.39.5