Ceph » CephFS

This idea has been discussed at Cephalocon2023. (Please refer to the conclusions page in https://static.sched.com/hosted_files/ceph2023/d9/Cephalocon2023_LINE_Optimizing_CephFS.pdf"

The bal_rank_mask (e.g., https://github.com/ceph/ceph/pull/43284) can separate unpinned subdirs within certain MDS ranks from pinned subdirs. But several subdirs are mixed in mds corresponding to bal_rank_mask, which can affect performance. For example, if there are a lot of files in the /backup and /image directories and bal_rank_mask 0xf is specified, the metadata will be dynamically distributed within 0~3. However, they can affect each other according to metadata movement.If each directory has the same workload, distributing /backup to rank 0-1 and /image to rank 2-3 will optimize performance. Therefore, per subdir rank mask is needed as ceph.dir.bal.mask vxattr. This feature allows a specific subdir to use specific multiple MDS ranks exclusively.

Usage
A target subdir is dynamically distributed within rank0 and 1.
$ setfattr –n ceph.dir.bal.mask –v 0x3 /cephfs/home/yongseok

Please refer to additional slides. https://github.com/yongseokoh/presentation/blob/main/A_New_Parititioning_for_CephFS.pdf