methinks that level 1, (which is what you can get in software) is mirrored raid. So total space = 1/2 total hard drive space. Yes you can run your system of it. I have done it before. (But with raid 0) If you have cash, and you have alot of data (which it seems you don't), and you need something that isn't level 1 or 0 (most people like 5, which is the parity drive you spoke of) then the XRAID is very good. 1TB = $5000. + it is really fast, and on fibre channel. In fact its so fast i don't think a quicksilver could even take up half the bandwidth avialbe on the thing. </END SALES PITCH>
But really, software RAID is a quick fix. You can't expand it with out eraseing it. And you only get 1 and 0.
2 cents