Power saving? (Score 2, Interesting)

I would also like to build such a thing, but a box full of disks spinning 24/7 is likely to use a lot of power and give off a lot of heat. Are there any power saving solutions to this? It would be nice if there was some intelligent software that, when you try to play a movie off the disk, spin up only the disk that has the file, read a large chunk of it into memory, and spin the disk back down.

Is this doable?