You are upgrading a Hadoop cluster from HDFS and MapReduce version 1 (MRv1) to one
running HDFS and MapReduce version 2 (MRv2) on YARN. You want to set and enforce a
block of 128MB for all new files written to the cluster after the upgrade. What should you
do?

A.
Set dfs.block.size to 134217728 on all the worker nodes, on all client machines, and on
the NameNode, and set the parameter to final.

B.
Set dfs.block.size to 134217728 on all the worker nodes and client machines, and set the
parameter to final. You do need to set this value on the NameNode.

C.
Set dfs.block.size to 128M on all the worker nodes and client machines, and set the
parameter to final. You do need to set this value on the NameNode.

D.
You cannot enforce this, since client code can always override this value.

E.
Set dfs.block.size to 128M on all the worker nodes, on all client machines, and on the
NameNode, and set the parameter to final.

Explanation: