HBase is one of the most popular databases in the Hadoop and NoSQL ecosystem. HBase is a highly-scaleable database that works with fulfilling the partition tolerance and availability of the CAP-Theorem. In case you aren’t familiar with the CAP-Theorem: the theorem states that requirements for a database are consistency, availability and partition tolerance. However, you can only have two of them and the third one comes with a trade-off.
HBase uses a Key/Value storage. The schema of a table in HBase is not present (schema-less), which gives you much more flexibility than with a traditional relational database. HBase takes care of the failover and sharding of data for you.
HBase uses HDFS as storage and ZooKeeper for the coordination. There are several region servers that are controlled by a master server. This is displayed in the next image.