Hi, @Saurabh Gupta; you can try reduce the number of replication factor, Below information may help you:
1, Modify ClusterB's hdfs replication factor.
vi $HADOOP_HOME/etc/hadoop/hdfs-site.xml
###
<property>
<name>dfs.replication</name>
<value>2</value>
</property>
###
2, Run distcp to replicate ClusterA's data into ClusterB
hadoop distctp -Ddfs.replication=2 -update -p hdfs://ClusterA:8020/ hdfs://ClusterB:8020/
3, If ClusterB already has existing data. Can run below command to release the space.
hdfs dfs -setrep -w 2 hdfs://ClusterB:8020/
That may reduce the total size of HDFS data.