Datanode Decommissioning from Hadoop Cluster

Hadoop offers the decommission feature to properly take out a set of existing data-nodes. The nodes to be taken out of cluster should be included into the exclude file, and the exclude file name should be specified as a configuration parameter dfs.hosts.exclude. This file should have been specified during namenode startup. It could be a zero length file. You must use the full hostname, ip or ip:port format in this file. Then the shell command

bin/hadoop dfsadmin -refreshNodes