The Failure of RAID
I once worked as a part-time IT manager at a small company. We did all the "good" things... purchased some reputable SCSI RAID controllers, did tape backups, etc. We actually switched back and forth between IDE and SCSI during my time there due to cost issues, each time being careful to implement a RAID setup.
However, every time we had a problem with our storage system, it was due to the RAID controller. I'm not sure we ever actually had a drive failure in the 8 years I worked there. Fortunately even the problems we had with the controllers were only close calls, never any actual data loss.
The first time, since SCSI disks was so expensive, we used RAID-5. However, what I discovered in attempting to restore (what appeared to be lost data at the time) was that RAID-5 would be one of the worst possible configurations, if you're attempting to recover the data on your disks. There is no standard format for how the data is stored on-disk. Which means every RAID controller vendor will have a different method of storing your data. In fact, in my case, the same vendor with the same model RAID controller had different (and incompatible) implementations. Your data is literally swiss cheese across multiple drives. (Try searching for a data recovery house that'll work with RAID-5 disks.) Fortunately, the vendor was still in business and their support was well enough that they got me a working firmware that allowed me to get back up to a running system in a matter of hours. But the point then was clear: RAID-5 is bad for data recovery.
Later on, I decided to use RAID-1, mirroring only. Unfortunately, I discovered the same problem. Different vendors would still had their own ways of storing the data.
The only solution that seemed to work best was software RAID. In particular Linux software RAID. (I presume Windows software RAID would have the same effect, but I have not tested that). Because the RAID implementation is done in software, you can be guaranteed the same algorithm across different hardware. The Linux implementation in particular has an added bonus where you can put the drive in a standalone system and it'll access it perfectly without any addition configuration of RAID sets or the like.
This of course greatly reduces your down time in the event of some horrible system failure. Just pop the drive (presuming it's still in working order) into a spare computer, and you're good to go.
For RAID to be truly useful, there must be a standard for the on-disk formatting of drives. Until then, I personally will only look at solutions that implement software RAID, preferably Linux.