Ceph monitors use leveldb to store all of the required monitor data for your cluster. This includes things such as the monitor map, OSD map, and PG map, which OSDs and clients pull from the monitors to be able to locate objects in the RADOS cluster. One particular feature that one should be aware of is that during a period where the health of the cluster doesn’t equal HEALTH_OK, the monitors do not discard any of the older cluster maps from its database. If the cluster is in a degraded state for an extended period of time and/or the cluster has a large number of OSDs, the monitor database can grow very large.
In normal operating conditions, the monitors are very lightweight on resource consumption; because of this, it’s quite common for smaller disk sizes to be used for the monitors. In the scenario where a degraded condition continues for an extended period, it’s possible...