Main Hadoop 2.0 daemons !

• NameNode : one per Namespace, stores & handles HDFS metadata
• Secondary NameNode : (for now) still in use if no HA
• Checkpoint node : (later) multiple checkpoint node is possible, performs periodic checkpoints
• Backup node / Standby node : allows high availability, keep updated copy of namespace in its memory (if using no checkpoint allowed)
• DataNode : stores HDFS data

• ResourceManager : a global pure scheduler
• ApplicationMaster : one per application, negociates ressource with RM, monitors and asks task execution to NodeManager 
• NodeManager : one per slave server, a task application container launcher and reporting agent
• Application Container : a separate processing unit, it can be a Map, a Reduce or a Storm Bolt, etc