Recently, we changed how HBase assigns regions. This architectural change is referred to as ZK-less region assignment, i.e. assigning regions without involving ZooKeeper. The change allows us to achieve greater scale as well as faster startups and assignment. It is simpler and has less code, improves the speed at which assignments run so we can do faster rolling restarts. The master is also re-architected to handle more regions. This feature will be on by default in HBase 2.0.0.