ZooKeeper reliability - three versus five nodes

Question

From the ZooKeeper FAQ:

Reliability:

A single ZooKeeper server (standalone) is essentially a coordinator with
no reliability (a single serving node failure          


        

Answer 1

Zookeeper requires that you have a quorum of servers up, where quorum is ceil(N/2). For a 3 server ensemble, that means 2 servers must be up at any time, for a 5 server ensemble, 3 servers need to be up at any time.