The page describing adding an arbiter should cover the appropriate options to minimize the footprint of an arbiter on a system. Here is the current page:

http://docs.mongodb.org/manual/tutorial/add-replica-set-arbiter/

I would suggest adding a section regarding the minimization of the process. Something like this, with an appropriate warning note:

Arbiter nodes do not store any data, but until the process is added to the set it is unaware of its special nature, and hence will start up with full sized journal and data files like any other node. To minimize this, the following options can be set to true:

WARNING: this is for arbiter nodes only, for production environments, these options should not generally be set on data bearing nodes.

• nojournal
• smallfiles
• noprealloc