Minor - P4 The range deleter unnecessarily logs on each work iteration, producing spam in the logs:
d20000| 2017-11-06T18:06:10.286-0500 I SHARDING [conn18] Scheduling immediate deletion of sbtest.move_chunk range [{ _id: 75000.0 }, { _id: MaxKey })
d20000| 2017-11-06T18:06:10.286-0500 I SHARDING [conn18] Waiting for cleanup of sbtest.move_chunk range [{ _id: 75000.0 }, { _id: MaxKey })
d20000| 2017-11-06T18:06:10.312-0500 I SHARDING [Collection Range Deleter] Deleted 128 documents in sbtest.move_chunk range [{ _id: 75000.0 }, { _id: MaxKey })
This logging should either be removed or set at a higher level.