If you continue reading the man page, I think you will find that the -u option is for updating the resource parameters of the specified cache directory (an existing cache fs).

If you are creating a new cfs, then continue reading the man page and associated man pages (at the bottom of the page you will SEE ALSO for commands associated with this. You should only have to put in the numbers you need to change what the default is (no, I don't know what the default is). See the examples in the man page for more info.