Large highly connected topologies and large clusters write a lot of data into ZooKeeper. The heartbeats, that make up the majority of this data, do not need to be persisted to disk. Pacemaker is intended to be a secure replacement for storing the heartbeats without changing anything within the heartbeats. In the future as more metrics are added in, we may want to look into switching it over to look more like Heron, where a metrics server is running for each node/topology. And can be used to aggregate/per-aggregate them in a more scalable manor.