Once you connect the 10 new data nodes to the cluster Ambari automatically distributes the common hadoop config file i.e hdfs-site.xml,Mapred-site.xml,yarn-site.xml etc to those new nodes so they can start receiving data blocks.
My suggestion as a workaround would be to add these 10 new datanodes hostnames FQDN or IP (separated by a newline character) in the dfs.exclude file on the NameNode machine, edit the <HADOOP_CONF_DIR>/dfs.exclude file and where <HADOOP_CONF_DIR> is the directory for storing the Hadoop configuration files. For example, /etc/hadoop/conf.
First, ensure the DNS resolution is working or your /etc/hosts are updated and the passwordless connection is working with those hosts. Once the 10 new nodes are in the dfs.exclude file the namenode will consider them as bad nodes so no data will be replicated to them as long as these hosts remain in the dfs.exclude file once you have updated the NameNode with the new set of excluded DataNodes.
On the NameNode host machine, execute the following command:
hdfs dfsadmin -refreshNodes
where <HDFS_USER> is the user owning the HDFS services
That should do the trick, once these hosts are visible in Ambari turn maintenance mode on so you don't receive any alerts
The day you will decide to add/enable these 10 new datanodes you will simply cp or mv the dfs.exclude to dfs.include file located <HADOOP_CONF_DIR>/dfs.include these nodes will start heartbeating and notifying the NameNode that thes DataNodes are ready to start receiving files and participating in the data distribution in the cluster.
On the NameNode host machine remember to execute the following command:
hdfs dfsadmin -refreshNodes
Don't forget to disable Maintenance mode on the new datanodes and remove them from dfs.exclude file if you didn't rename or delete it.
Run the HDFS Balancer a tool for balancing the data across the storage devices of an HDFS cluster.
sudo -u hdfs hdfs balancer
The above balancer command has a couple of options either threshold or again the dfs.include and dfs.exclude see explanation below
Include and Exclude Lists
When the include list is non-empty, only the datanodes specified in the list are balanced by the HDFS Balancer. An empty include list means including all the datanodes in the cluster. The default value is an empty list.
[-include [-f <hosts-file> | <comma-separated list of hosts>]]
The datanodes specified in the exclude list are excluded so that the HDFS Balancer does not balance those datanodes. An empty exclude list means that no datanodes are excluded. When a datanode is specified in both in the include list and the exclude list, the datanode is excluded. The default value is an empty list.
[-exclude [-f <hosts-file> | <comma-separated list of hosts>]]
If no dfs.include file is specified, all DataNodes are considered to be included in the cluster (unless excluded explicitly in the dfs.exclude file). The dfs.hosts and dfs.hosts.exclude properties in hdfs-site.xml are used to specify the dfs.include and dfs.exclude files.
Hope that helps