What is the maximum sentence for the possesion of crack cocaine?

Depends where you live and how much of it (crack) you posses. If you are caught (hopefully not with much) then you can argue its 'personal' i.e. Your personal stash, and not for re-sale.

In the UK they allow personal (1-3 grams) and a slap on the wrist. They say "possesion is 7 years" but that's complete and utter bullsh*t.