Yeah, a feature's going to take up much more space than a short.
On set:
You really should have at least a RAID 1 system for your backup, so if you're planning 2TB of hard drive space, you really need 2x 2TB drives for a RAID 1 system, plus an extra 2 in case of hard drive failure... Then you should also probably have another two non-raided 2TB drives that you can give to other crew - one should go with the Producer, one with someone else, and the RAID cage/drives with you - if you take everything and you write off your car in a crash on the way home, you'll not only have a car, but you'll have potentially lost all the footage you just shot.
All these drives/cages should be of at least FW800 speed. You should also set up a UPS for your on set computer/drive rig.
Your editing working drives should be seperate from the on set backup drives.
HDD space is not expensive, but if you want to be thorough with your backups it starts to add up. These are the methods we use on shows that can't afford the entire DIT cart/rigs that include full blown Mac Pros, Raid 5 arrays etc.
You don't have to go all out, but I'd suggest on set at least a RAID 1 system, preferrably Solid State if you can afford it. You can probably get away with such a setup for editing as well, though I've seen standard external drives used for editing, though I've also seen entire NAS RAID arrays at some post houses....
Back to space: on an Alexa shooting compressed ProRes 4444, you get ~11 minutes of footage on a 32GB card, obviously that's significantly higher shooting uncompressed HD, or ARRIRAW.
On an Epic, you get ~30 minutes shooting with 5:1 compression in 4k HD on a 128GB card.
So, what's your shooting ratio? How long's the final film? How much do you want to compress, if at all? Are you shooting HD or higher? How many redundancies are you thinking of creating..?
