what is a split brain , when one zookeeper server fail from total 3 zookeepers

Question

We have 3 zookeepers servers, and 6 Kafka machines. What could be when one zookeeper server fail, and we have now only two zookeeper servers, what is the chance to get "split brain"?

As I understand when we get a split brain, then the two zookeepers that still alive actually not working as should be.

Answer 1

In ZooKeeper, an even number of peers is supported, but it is normally not used because an even sized ensemble requires, proportionally, more peers to form a quorum than an odd sized ensemble requires. For example, an ensemble with 4 peers requires 3 to form a quorum, while an ensemble with 5 also requires 3 to form a quorum. Thus, an ensemble of 5 allows 2 peers to fail and still maintain quorum, and thus is more fault tolerant than the ensemble of 4, which allows only 1 down peer.

So in your case with 3 ensemble, it will support only 1 node failure, as with remaining 2 , it can't form a quorum