My personal experience is you're increasing your chances of losing data by going to Raid setup. In my case I had a Raid 5+1 array. It was run from a dedicated Raid controller card and it had an onboard battery pack that went dead and corrupted the array. Of course I thought it was 20 other things until I figured out that was the problem.(I had to buy another controller card and when it worked I realized it was the original card, until then it looked like so many other things were the problem) I also never got it to work as I hoped, where I would have 3 sets of drives, 2 active, and one out of the computer as a backup. I hoped to be able to pull out one set every week, put the other one in and have it autoupdate the older array. That just never worked right. You also have a lot more noise and heat. Make sure you have a helluva case with lots of fans, those hard drives will get hot hot especially all packed together. My setup was fairly robust corporate stuff and when it failed I was left not trusting raid.
Always go with the KISS method, keep it simple stupid. Raid is not simple. There's way more that can go wrong and you're lured in with this false sense of security. "I'll be ok if a drive or even two fail." Yeah but what if your power fails, do you have a backup that will run the computer for a while. FYI I did, but still the onboard battery pack got me. What if you're not there when the power fails and you don't get it shut down before your backup runs out, etc., just a lot that can go wrong. To me most consumer raid stuff today is made to access your data fast, not as any kind of backup solution. It's for video editing where you need to keep a ton of data on the computer, have fast scratch disks etc, but you can bet that data is also backed up safely somewhere else.
KISS method for me means backing up to an external hard drive. As another poster said, esata is where it's at now for speed, but USB2.0 is much more universal. I can take the USB enclosure to any computer I have and copy to or from. I never bother screwing the enclosure together, because i'm always swapping hard drive in and out of it.
I also burn 2 sets of DVD's and store in 2 seperate places, One offsite. Thus far my worse case has been a hard drive failure, and out of 50 or so DVD's that was used to restore it, 2 had a handful of unreadable files on them. The 2nd set of dvd's read those files just fine and I then remade the bad dvd's. The point is, all of this stuff fails so have multiple redundancy.
I organize my stuff in a folder by date so it might say "2007-04-08 Easter at so and so's.", I then run a dos command (in windows click start, then run, then type in "cmd" to get a dos prompt. Then d: to get to the root directory of the D drive for instance.)
dir /B *.* > c:\list.txt
that spits out all the folders and files in the root directory of whatever drive you're on to a text file in the root of the c drive. If you want all the file names in the subdirectories, basically everything on the disk, add a /S to that.
I then cut and paste that into a master text file. I put the hard drive into the little static proof bag it came in, and put a sticker on the outside with a number. So then I can look at my text file(or better yet search through it) and see that hard drive so and so has this or that shoot on it. Get it out, plug into enclosure and have the files copied back to the main computer in minutes.
I've read several advice things that say it's good to do a scandisk on your hard drives, say every 6 months. The longer they sit not being used the more likely they'll get errors. They have error correction built into them so when you run the scandisk the hard drives will find tiny errors and self correct them using it's parity data.
The problem I have is when a hard drive fails, it's really getting to be a chore to back up from dvd's. A 500gb drive means you're going to be spending a lot of time copying the contents of 100+ dvd's over. Luckily I have 4 computers around the house with dvd drives, but that's still a day of poking dvd's in and out and then copying to a replacement drive in an enclosure. Hopefully another year or so and we'll have Blu Ray or HD DVD writable disks that will hold a lot more data.