Scratch disk; one for all....and all for one.

Ok this is concerning Final Cut Pro 7 running on a 2008 3.0GHz iMac.

I need to keep this system as simple as possible for reasons not worth getting in to. It is for casual editing, and for the most part using HD content from AVCHD, transferred to Pro Res 422 LT.

I would just like to hear a few seasoned pro's opinions on using one big drive for both capturing, storing and editing footage to/from. The idea is to buy an Icy Dock dual bay sata enclosure, put two Seagate Barracuda 7200rpm drives in it, and set it to see them as individual drives. One will be the scratch disk, the other will be used to clone the scratch disk at the end of each day/week. It could be set to RAID 1 but for casual use that seems like more writing to disk than necessary. It will connect via firewire 800 (unless someone can tell me how to make an external eSata connection from a 2008 imac). I know I could buy two external drives but the price would be much the same anyway and the desk would be more cluttered. Also this way we can change drives if we ever need to.

What I'm asking is (and I know this isn't the way a pro would set the system up) is it "ok" to use one scratch disk for capturing storing and editing to/from, for casual use...? Or will it be too much for the disk?

Thanks guys.