RAID is just a general term for a number of different hard drive management techniques.
Mirrored is not an alternate to RAID, it is in fact a form of RAID - Mirror is RAID 1.
A list of all the RAID levels can be read from Wikipedia.
Based on the mirror, basically, if one hard drive fails the other one should be able to pick up the slack.
The higher the quality of the RAID controller, the better the features
* - for example, on budget models, if a drive was to fail during a write, it would be corrupt... On higher quality cards, it is possible that they contain some sort of cache/memory of their own and if it detects that a failure occurred, it will automatically write to the other drive (very smart stuff!)
RAID is not a property of a filesystem, you usually set up the RAID level on a RAW hard drive using some sort of manager, then, you will use the hard drive like normal with all the "magic" being done in the background - so - it is completely filesystem independent.
* As well as controllers, there is of course software RAID, this typically has the lowest features and is a CPU hog as there is no offloading, but, it can work well!