The failure of which daemon makes HDFS unavailable on a cluster running MapReduce v1
(MRv1)?

A.
Node Manager

B.
Application Manager

C.
Resource Manager

D.
Secondary NameNode

E.
NameNode

F.
DataNode

Explanation:
The NameNode is the centerpiece of an HDFS file system. It keeps the directory
tree of all files in the file system, and tracks where across the cluster the file data is kept. It does
not store the data of these files itself. There is only One NameNode process run on any hadoop
cluster. NameNode runs on its own JVM process. In a typical production cluster its run on a
separate machine. The NameNode is a Single Point of Failure for the HDFS Cluster. When the
NameNode goes down, the file system goes offline.
24 Interview Questions & Answers for Hadoop MapReduce developers, What is a
NameNode? How many instances of NameNode run on a Hadoop Cluster?