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

Basically, Zookeeper will work just fine as long as Active Zookeepers are in MAJORITY compared to failed Zookeepers. Also, in case of even quorum size i.e 2,4,6 etc. Failed = Active, because of that its not recommended.

Both 3 and 4 will handle only 1 faliures then why whould we want to used 4 Zookeepers instead of 3.

Answer 2

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.