There are different levels of RAID, some are more for data security/stability, some are more for speed. To be honest, it's a discussion that's a little beyond the Travel Technology forum IMO. You can definitely do it yourself, but you'll need to do a fair bit of reading. Google is definitely your friend on this.

If data security (from a redundancy standpoint, not a snooping standpoint) is not a big concern, you'd probably be better off just buying one of the pre-build NAS (network attached storage) units that are now being sold. It'll likely be cheaper and considerably easier.