don't rely on a raid type of system to be fool proof. you still need to have a separate disk outside of your local/nas setup to be fault tolerant. i have been in the computer industry for over 30 years from mainframes down to pc's. even the companies using the largest and the most expensive raid storage systems back up their data to other disk systems or to tape. if you rip your cd's to the nas/raid system, keep your original cd's as your backup if anything happens. disks do fail and the raid setup allows for a disk drive to fail without corrupting your data (if you use raid 1, 5, 6). with a computer systems, you usually have 1 interface (controller) to the storage system and they sometimes fail sending bad data to the disk subsystem. to help alleviate this, you need 2 controllers to the disks or backup your data to another device outside of your computer.