Do you currently do backups to offline media? If not, then that's what you should be doing. There are lots of risks to your data that RAID won't protect against. Good backup strategy means keeping at least TWO copies of your data on OFFLINE media, one of which is stored OFFSITE.
With a combination of software and hardware raid you can do this, but don't. Like sminial says keep the best stuff offline. If you insist on data integrity inside your case, raid 1 with two 1.5 tb drives. Or just get one 1.5 tb drive and a HD toaster and antistatic bag. Store your most important stuff on one of those drives, disconnect it and only connect it every once in a while to copy new stuff onto it. One lightning stike can kill a raid 1. One house fire can get the offline drive in your closet too. It just depends on how paranoid you are or want to be.