Disk arrays, which organize multiple, independent disks into a large, high-performance logical disk, were a natural solution to dealing with constraints on performance and reliability of single disk drives. The term "RAID" was invented by David Patterson, Garth A. Gibson, and Randy Katz at the University of California, Berkeley in 1987. In their June 1988 paper "A Case for Redundant Arrays of Inexpensive Disks (RAID)" they argued that the top performing mainframe disk drives of the time could be beaten on performance by an array of the inexpensive drives that had been developed for the growing personal computer market. Although failures would rise in proportion to the number of drives, by configuring for redundancy, the reliability of an array could far exceed that of any large single drive.
In 1994 Peter Chen together with Ed Lee and the Berkeley team wrote a computer survey paper that lays out in great detail the background case for disk arrays and goes into the details of the various RAID models.
RAID: High-Performance, Reliable Secondary Storage Peter Chen, Edward Lee, Garth Gibson, Randy Katz and David Patterson, ACM Computing Surveys, Vol 26, No. 2, June 1994.