Hadoop software library is a framework that allows for the distributed processing of large data sets.It is designed to scale up from single servers to thousands of machines, each offering local computation and storage, Rather than rely on hardware to deliver high-availability, the library itself is designed to detect and handle failures at the application layer.It can store data in raw or any of the serialized formats like Avro, SequenceFile etc
The Apache Cassandra is a database which provides scalability and high availability without compromising performance. Linear scalability and proven fault-tolerance on commodity hardware or cloud infrastructure make it the perfect platform suited to point lookups and wide tables. Cassandras support for replicating across multiple datacenters makes it a class apart
Apache HBase is the Hadoop database that can be very useful for range scan based batch processing of records. The main features of HBase database is Linear and modular scalability,Strictly consistent reads and writes,Convenient base classes for backing Hadoop MapReduce jobs with Apache HBase tables and Easy to use Java API for client access.
Aerospike's Database is Mostly suited for real time queries on large volumes of analytic information. Aerospike is a distributed, scalable NoSQL database,Aerospike's Java client enables you to build applications in Java that store and retrieve data from an Aerospike cluster.It contains both synchronous and asynchronous calls to the database