Thomgeo1, I prefer to have my OS and may data on 2 entirely different subsystems. This gives me the option of moving my Data Raid Subsystem to another machine easily if I have to.
I mirror the OS/Application drives for speed and redundancy; the data drives which hold ALL of my data, including USER My Documents, and all the practice data, images/scans, database etc, are on a raid five.
My entire raid5 subsystem is backed up incrementally to a Promise NAS N4300 (also RAID5). The OS drive (RAID 0) is IMAGED weekly. The Data backups are stored online. The images are bootable images on DVD.