Differences in each hadoop version

Hadoop 2.x is developed from hadoop-1.x, with the significant features over hadoop-1.x:

• HDFS HA for NameNode (manual failover)
• NextGen MapReduce (YARN)
• HDFS Federation
• Performance
• Wire-compatibility for both HDFS and YARN/MapReduce (using protobufs)

Hadoop 0.23.x is a trunk which contains:

• HDFS Federation
• NextGen MapReduce (YARN)

Hadoop 1.x is developed from hadoop 0.20-security code support for:

• security
• HBase (append/hsynch/hflush, and security)
• webhdfs (with full support for security)
• performance enhanced access to local files for HBase
• other performance enhancements, bug fixes, and features