Which command does Hadoop offer to discover missing or corrupt HDFS data?

A.
The map-only checksum utility,

B.
Fsck

C.
Du

D.
Dskchk

E.
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.

Explanation:
HDFS supports fsck command to check for various inconsistencies. It it is designed
for reporting problems with various files, for e.g. missing blocks for a file or under replicated
blocks. Unlike a traditional fsck utility for native filesystems, this command does not correct the
errors it detects. Normally Namenode automatically corrects most of the recoverable failures.
HDFS’ fsck is not a Hadoop shell command. It can be run as ‘bin/hadoop fsck’. Fsck can be run on
the whole filesystem or on a subset of files.

Hadoop DFS User Guide