Balance data in a federation
Depending on your requirements, you can use the HDFS Balancer to balance data either at the level of the DataNodes or the block pools in a cluster with federated NameNodes.
Run the Balancer using the
hadoop-daemon.sh start balancer [-policy <policy>]
Specify either of the following values for policy:
datanode: The default policy that balances data at the level of the DataNode.
blockpool: Balances data at the level of the block pool.