@AA MJ, How many datanodes do you have in cluster ? As per message , it seams you only have one datanode. Ideally, you should have 3 datanodes atleast to manage replication correctly.
However, as per this message it means that you have only one data node and that data node is excluded. Can you please check content of /etc/hadoop/conf/dfs.hosts.exclude ? If the datanode is added to exclude host list, this behavior is expected.
If data node is not added to exclude list and still you are noticing issue with replication, you can restart the datanode and try again.