Anything wrong with putting the RAW and Derivative Files on the Same Hard Drive?

Hi Everybody
I'm getting ready to make the leap to a systematized DAM-based workflow. I still have a couple basic questions
I'll be following Peter's advice by having my initially ingested files on consecutive folders, in my case called "INGEST_018_080301", within an "Initial Ingest 01" folder on a data hard drive, and then the Derivative files in separate sequential folders, such as "WKD_047 within a "Worked 01" folder. But I'd like to have both of those folders on the same hard drive, say called "IMAGES 01". When the entire drive is full, I'd set up the next drive and call it "IMAGES 02" with the "Initial Ingest 02" and "Worked 02" folders on it.
This would make my hard drive backups simple with a 1-1 volume sync and mean I'd have to use fewer slots in my 5-bay eSATA box, leaving me more slots for backup and more open slots for when I'd be inserting my offsite 1-1 sync volumes. Once I have 5 bays permanently occupied I'd probably need to add another eSATA box.

Any thoughts from other users?

Andy