The reduce command only allows  you to take away storage space that is not
in use by your database. The amount of data in the database is determined by
the number of files backed up and archived, the number of clients, the
number of versions, the number of scripts, etc.  Typically, the size of your
database only grows, never shrinks, unless you decrease one or more of the
above. What's the reason you want to reduce in the first place?