Eh...
Okay. To set things straight:
On the harddrive that comes in your xbox, there is, by default, a C Partition (called System, bout 400mb), E Partition (User Save, bout 5 gigs), X, Y and Z partitions (Temporary Cache Partitions, 700mb each).
(those were from memory, go ahead and correct me if they are off)
When the xbox was first released, it shipped with a Western Digital 8gb Harddrive, and these partitions took up the entire drive. Later, newer xboxes shipped with 10gb harddrives, but the same partitioning system was used and only 8gb are accessable. Adding the "F" drive / partition allows you to use those other 2gb on a default drive.
On an upgraded harddrive, you format the first 8 gb with the default partitions, then you HAVE to add the F drive in order to access the rest of the space on it.
This F partition is purely for storing media and game backups, as it is not used by official xbox software in any way.
You do not have to have an unlocked drive to format or use this partition. It won't format at all if you only have an 8gb so no worries.
roofus