Which of the following commands does Hadoop offer to discover missing or corrupt HDFS data?

A.
Hadoop does not provide any tools to discover missing or corrupt data; there is no need
because three replicas are kept for each data block.

B.
dskchk

C.
du

D.
fsck

E.
The map-only checksum utility.

Explanation:
http://docs.hortonworks.com/CURRENT/index.htm#Monitoring_HDP/Using_Nagios_With_Hadoop/
Nagios_Alerts_For_Hadoop_Services.htm (Corrupt/missing block alert, Possible remedies, third
bulleted point)