You want to see which datanodes are active underlying a given hdfs system. You also want to know statistics about the storage usage. If you are regularly adding data to your hdfs system, you want to stay below 70% utilization. If you want your hdfs system to perform well but you are not regularly adding new files, you want to stay under 80%. How do you find out about the storage usage of your datanodes that support your hdfs system?
Run this command:
hdfs dfsadmin -report
# or this command below
sudo /usr/local/hadoop/bin/hdfs dfsadmin -report