HOWTO: Check the Health of an HDFS Cluster
How do I check the health of my HDFS cluster (name node and all data nodes)?
Hadoop includes the dfsadmin command line tool for HDFS administration functionality. This tool allows the user to view the status of the HDFS cluster.
To view a comprehensive status report, execute the following command:
hadoop dfsadmin -report
This command will output basic statistics of the cluster health. This includes the status of the namenode, status of each datanode, disk capacity amounts, block health statuses.
The same information can be found on the NameNode web status page – at http://<namenode IP>:50070/dfshealth.jsp