Mongorestore allows for the number of concurrent insertion workers per collection to be increased using the --numInsertionWorkersPerCollection option.

However, this is not available for mongomirror -- while you can increase the number of collections copied in parallel (--numParallelCollections), there's no parameter surfaced to allow more inserts to be occurring at the same time over multiple threads within each collection.

|t would be helpful to have a parameter like this to use to increase parallelization in order to increase the speed of migrations of large collections.