Cluster Summary: 45 files and directories, 12 blocks = 57 total. Heap size is 15.31
MB/193.38MB(7%) Refer to the above screenshot. You configure a Hadoop cluster with
seven DataNodes and on of your monitoring UIs displays the details shown in the exhibit.
What does the this tell you?

A.
The DataNode JVM on one host is not active

B.
Because your under-replicated blocks count matches the Live Nodes, one node is dead,
and your DFS Used % equals 0%, you can’t be certain that your cluster has all the data
you’ve written it.

C.
Your cluster has lost all HDFS data which had bocks stored on the dead DatNode

D.
The HDFS cluster is in safe mode