Many things can cause a drive failure. Power interrupt, drive enclosure failure, drive mechanisms and even outside elements like fire or water damage can all cause us to lose our data. The first thing you have to do is get your head around the fact that all drives fail at sometime no matter what the cause. It can be a low cost single desktop enclosure or a very expensive sophisticated RAID system. Its not a matter of IF they fail, its WHEN they fail.
The golden backup rule is to have your data in at least three places. The storage where you work from and two sets of backups, with one backup set being off site in case of a disaster. I don't care if you use DVDs, CDs or hard drives for your backup, you must backup or risk losing your data forever.
Small redundant RAID systems are all right but they require you to have extra drives on site and if they do work on the rebuild you may still be rebuilding corrupt data. With that in mind you should not be focusing on this as a backup solution. You should still have a real back up of your files on another set of media. This will prevent you having only one single version of the data even if it becomes corrupt.
Since the RAID system consist of regular drives inside, hence the acronym "Redundant Array of Inexpensive Disks" they can fail like any other drive. So instead of focusing my resources on a RAID drive for redundancy, and a lot of money, I use a large desktop drive for my working storage and a set of external drives for my redundancy and backup and plan for my drive to fail. Knowing and planning for your drive to fail will keep you in a better place when it does happen and you'll be prepared.
I have had my share of drive failures and its no fun and can be very expensive. I was not impressed by the RAID systems I bought in the past so I decided to not worry about the drive as much as the back up plan. The backup I utilize is with a drive enclosure by WiebeTech, the RTX-100, which houses a single SATA drive enclosure. (They aalso make multi-drive enclosures.) I use the WiebeTech drive with Retrospect software, much like DAT tapes in the past, and store the backup data on 500GB drives and use as many as needed to continue my backup. I also have an off-site backup set for my my weekly backup in case of a fire at my studio. In the event of a disaster at the studio I'm out one week of work, otherwise it gets backed up everyday on another set I keep in the studio. A good rule of thumb is to back up as often as you don't mind replacing the work. If you don't mind replacing a week's worth of work then back up only once a week. If you only want to lose a day's worth of work then backup everyday. For the hyper paranoid types on a Macintosh system you can use Apple's Time Machine to backup which saves multiple versions as you work.
So the real problem is, how fast can you get your data back when a drive fails? That's the real test. When a drive goes down, and it will, the real test is how fast can you be back up and running with your lost data. Will you have to wait for someone to recover your data off of the failed drive (maybe a week or two plus $1000-$2000 in costs)? Will you have to wait for the rebuild of your RAID drive (maybe 2-6 hours provided you have a drive on hand)? Or will it be stored on a drive that is on hand sitting in your studio waiting to be mounted to your computer?
With the drive enclosures I can store a good amount of data for a good price. The drive enclosure runs about $225 which is less than what a 2TB drive costs but it gives me the flexibility a single drive does not. After the first $225 for the drive enclosure I can buy 500GB SATA drives to go in the enclosure for under $50. So now I can have two sets of 2TB of storage for just under $650. Add another 2TB for $200 to have another point of backup or even for an archive to clean off data from your drive. The more you use the more you save.
With this strategy I fill up drives as I continue the incremental backup and maybe twice a year I recycle the drives and start a new backup set again. Not only does this give you flexibility for storage since your backup size can unlimited the drives are fast and with the triple interface WiebeTech drive I can get through my backup fairly fast.
Once you do have a backup in place be sure to test it. You do not want to find out the backup didn't work or didn't backup as planned when you really need it after a drive failure. In fact, its a good idea to test it occasionally to make sure everything is working fine.
Asking yourself how fast and easy you can access your data once a drive fails is how I approach the backup system and shows how well you are prepared for a drive failure.
There's an old saying, "There are those who backup and there are those who have not lost their data yet.". Which one are you?