Compare the hardware requirements of the NameNode with that of the DataNodes in a Hadoop
cluster running MapReduce v1 (MRv1):

A.
The NameNode requires more memory and requires greater disk capacity than the DataNodes.

B.
The NameNode and DataNodes should the same hardware configuration.

C.
The NameNode requires more memory and no disk drives.

D.
The NameNode requires more memory but less disk capacity.

E.
The NameNode requires less memory and less disk capacity than the DataNodes.

Explanation:
Note:
* 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. Client applications talk to the NameNode whenever they
wish to locate a file, or when they want to add/copy/move/delete a file. The NameNode responds
the successful requests by returning a list of relevant DataNode servers where the data lives.
* A DataNode stores data in the Hadoop File System HDFS. There is only One DataNode process
run on any hadoop slave node. DataNode runs on its own JVM process. On startup, a DataNode
connects to the NameNode. DataNode instances can talk to each other, this is mostly during
replicating data.
24 Interview Questions & Answers for Hadoop MapReduce developers