Can anyone here confirm for me what is the total disk space requirements for a full ethereum blockchain synchronization using geth --fast?

I dont want to close geth and open Mist client to see if its synched or not, because the geth with the --fast switch supposed to be ran in one swoop and if I somewhat interrupt the --fast sync then I have to start all over again.

So, how do I tell if geth has finished syncing [without interrupting the current geth running process]?