Why HDFS Cluster needs High Availability : At the end of this topic you will understand idea behind setting up High Availability and how you should prepare for CCA-500 Exam Questions , idea is you shouldn't be confused about any of the trick questions that may come in exam so if you are clear on concepts and design in depth detail then you wouldn't fail the exam. If you are familiar with HDFS Cluster components, you need two types of Nodes to run the HDFS : Name Node Data Node If you are using a standard configuration, running just one NameNode is a single point of failure in an HDFS cluster. Each cluster has a single NameNode, and if that host or process became unavailable, the cluster as a whole is unavailable until the NameNode is either restarted or brought up on a new host. We can prevent the Single point of failure by running two Name Nodes in High availability mode - one as " Active " node and secondary Name node as " Passive " nod