mongod currently creates/uses subdirectories under the dbpath:

• journal
• _tmp - used by external sorter
• moveChunk - used by sharding
• rollback - used for rollbacks

Specifying journalPath is already covered by SERVER-13455.

For a number of reasons it would be desirable to make these paths user defined. One case would be when applying security and/or encryption policies for these directories.

Note that currently the _tmp directory will be removed when the server starts. This can also be problematic when attempting to apply such a policy.