The following figure represents the layout information of HBase on top of Hadoop:

There is more than one ZooKeeper in the setup, which provides high availability of master status; a RegionServer may contain multiple rations. The RegionServers run on the machines where DataNodes run. There can be as many RegionServers as DataNodes. RegionServers can have multiple HRegions; one HRegion can have one HLog and multiple HFiles with its associate's MemStore.

HBase can be seen as a master-slave database where the master is called HMaster, which is responsible for coordination between client application and HRegionServer. It is also responsible for monitoring and recording metadata changes and management. Slaves are called HRegionServers, which serve the actual tables in form of regions. These regions are the basic building blocks of the HBase tables, which contain distribution of tables. So, HMaster and RegionServer work in coordination to serve the HBase tables and HBase cluster.

Usually, HMaster is co-hosted with Hadoop NameNode daemon process on a server and communicates to DataNode daemon for reading and writing data on HDFS. The RegionServer runs or is co-hosted on the Hadoop DataNodes.