What is RAID and why is it so good?
RAID (redundant array of independent disks)  provides a way of storing the same data in different places (thus, redundantly) on multiple hard disks. This is good for several reasons. Most obvious is that it allows for all data to be safely copied and backed up in case of hardware failure. The other benefit is that during a read on a RAID array you should see a significant increase in speed in recalling data over that of single drive performance.