I have a new 2011 MBP with Lion. I recently found a firewire 800 HDD enclosure that I thought would be good for time machine backups. The internal HDD of my MBP is 750GB, with 400GB of it going towards Lion, the other 250GB for the bootcamp partition. When time machine does a backup, does it backup the entire HDD, or just the Mac partition? That way I know what size drive to buy (750GB vs 500GB).