@kotesh banoth
New data will be replicated to the newly added data node. But if you want to rebalance your cluster then it is best if you run the "HDFS Rebalancer" from ambari UI or via command line.
HDFS provides a “balancer” utility to help balance the blocks across DataNodes in the cluster.
Ambari UI --> HDFS --> Service Actions --> HDFS Rebalance<br>
(OR)
# su - hdfs -c "hdfs --config /usr/hdp/current/hadoop-client/conf balancer -threshold 10"
https://docs.hortonworks.com/HDPDocuments/Ambari-2.6.0.0/bk_ambari-operations/content/rebalancing_hd...