HDFS supports fsck command to check for various inconsistencies.
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.
Hope you understand.