RAID is a term from the old days of computers, simular to SCSI in that way. it stands for Redundent Array of Inexpensive Disks. RAID is a way of allowing multiple drives to act as one, and to provide data protection.
RAID 0 Mirroring, takes one drive set and duplicates it to another drive set as data is written. Requires a minimum of 2 drives of equal size. Used for data integrety.
RAID 1 Striping, takes the drives assiged and makes them all one volume, using full capacity. Data is written to all disc at the same time, spreading the bits over all disk. That is where the speed increase comes from. Used for Speed. Requires 2 drives minimum and all of same size.
RAID 3 Mirror with parity, Same as Level 0, but also reserves one dedicated disk for error correction data. It provides good performance and some level of fault tolerance Requires 3 drives minimum.
RAID 5 Stripping with Parity, Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance requires 4 drives minmum. One drive volume in space is used for the parity info, so that volume space is lost.
As to your question, that would be the case, but not as you see it. The only way for the data to be accessed to to have the primary drive of the RAID set die, and then the other drive would be used. Other way is to move the drive to a standard IDE port off of the RAID controller. The two drives are exact copies of each other.
Hope that helps.