> Built-in replication without the need to run Zookeeper, with multi-tier sharding support. They rewrite the ZK protocol using multi-paxos within CH itself. It's great.

AFAIK this description is kind of misleading. When they say that they got rid of Zookeeper people expect that they can just connect clickhouse nodes to each other and the replication will work. But that is not how things work - you still have to run external service called clickhouse-keeper. Basically what they did is they rewrote Zookeeper in C++.