Hadoop is very flexible and it is possible to integrate almost any kind of database into the system. Many database vendors extended their products to work with Hadoop. One database that is often used with Hadoop is Apache Cassandra. Cassandra isn’t part of the Hadoop project itself but is often seen in connection with Hadoop projects.
Cassandra comes with several benefits. First, it is a NoSQL-Database as well, working with a key/value store. Beeing developed by Facebook initially, it is now maintained by Datastax. Cassandra comes with a great performance and linear scalability.