In my experience, it is designed for functionality!!
RAID 0+1 and the other lower levels of RAID in the IDE environment allow for striping and data redundancy over simple volumes and multiple volumes. Where with only one drive, or even multiple drives (but not in RAID), it would only allow for storage!!
Edblor
Also take into account the SCSI RAID environment...where the controllers have lots of RAM onboard for data caching. IDE RAID has nothing of the sort (AFAIK). With the added RAM onboard the RAID controller, access time is as fast as the SCSI bus can access the RAM, not the physical drive!