A proper Ceph cluster comprises three or more Monitor daemons, ideally situated on distinct physical servers. If a cluster's MONs cannot form a quorum, which happens if not enough of the provisioned MONs are up, then new clients won't be able to connect to the system. Worse yet, existing clients will no longer be able to perform operations once their sessions expire. It is paramount for cluster health to have a majority of MONs up and able to fulfill their quorum duties.