Ceph: Designing and Implementing Scalable Storage Systems

MON quorum status

The concept of quorum is fundamental to all consensus algorithms that are designed to access information in a fault-tolerant distributed system. The minimum number of votes necessary to achieve consensus among a set of nodes is called a quorum. In Ceph's case, MONs are exploited to persist operations that result in a change of the cluster state. They need to agree to the global order of operations and register them synchronously. Hence, an active quorum of MON nodes is important in order to make progress. To keep a cluster operational, the quorum (or majority) of MON nodes needs to be available at all times. Mathematically, it means we need (n/2)+1 MON nodes available at all times, where n is the total number of MONs provisioned. ...