Fastest way to move Collection from Sharded MongoDB Cluster to a another Sharded MongoDB Cluster
As per MongoDB documentation  Create Chunks in a Sharded Cluster


  If you want to ingest a large volume of data into a cluster that is
  unbalanced, or where the ingestion of data will lead to data
  imbalance, such as with monotonically increasing or decreasing shard
  keys. Pre-splitting the chunks of an empty sharded collection can help
  with the throughput in these cases.


EXAMPLE

To create chunks for documents in the myapp.users collection using the email field as the shard key, use the following operation in the mongo shell:

for ( var x=97; x&lt;97+26; x++ ){
    for ( var y=97; y&lt;97+26; y+=6 ) {
        var prefix = String.fromCharCode(x) + String.fromCharCode(y);
        db.adminCommand( { split: "myapp.users", middle: { email : prefix } } );
    }
}


This assumes a collection size of 100 million documents.