MDS Memory Cache Limit

MDS servers keep their metadata in a separate storage pool, named cephfs_metadata and are the users of Ceph OSDs.

For Ceph File Systems, MDS servers support an entire IBM Storage Ceph cluster, not just a single storage device within the storage cluster. As a result, their memory requirements can be significant. This is the case particularly if the workload consists of small-to-medium-size files, where the ratio of metadata to data is higher.

For example, to set the mds_cache_memory_limit to 2000000000 bytes, run:

ceph_conf_overrides:
  mds:
    mds_cache_memory_limit=2000000000

Note: For a large IBM Storage Ceph cluster with a metadata-intensive workload, do not put an MDS server on the same node as other memory-intensive services. Doing so gives you the option to allocate more memory to MDS, for example, sizes greater than 100 GB.

For more information, see Metadata Server cache size limits.