History
Norman Ken Ouchi at IBM was awarded a 1978 U.S. patent 4,092,732 titled "System for recovering data stored in failed memory unit." The claims for this patent describe what would later be termed RAID 5 with full stripe writes. This 1978 patent also mentions that drive mirroring or duplexing (what would later be termed RAID 1) and protection with dedicated parity (that would later be termed RAID 4) were prior art at that time.
In October 1986, the IBM S/38 announced "checksum" - an operating system software level implementation of what became RAID-5. The S/38 "scatter-loaded" data over all disks for better performance and ease of use. As a result, a single disk failure forced the restore of the entire system. With S/38 checksum, when a disk failed, the system stopped and was powered off. Under maintenance, the bad disk was replaced and the new disk was fully recovered using RAID parity bits. While checksum had 10%-30% overhead and was not concurrent recovery, non-concurrent recovery was still a far better solution than a reload of the entire system. With 30% overhead and the then high expense of extra disk, few customers implemented checksum.
The term RAID was first defined by David A. Patterson, Garth A. Gibson and Randy Katz at the University of California, Berkeley, in 1987. They studied the possibility of using two or more drives to appear as a single device to the host system and published a paper: "A Case for Redundant Arrays of Inexpensive Disks (RAID)" in June 1988 at the SIGMOD conference.
This specification suggested a number of prototype RAID levels, or combinations of drives. Each had theoretical advantages and disadvantages. Over the years, different implementations of the RAID concept have appeared. Most differ substantially from the original idealized RAID levels, but the numbered names have remained. This can be confusing, since one implementation of RAID 5, for example, can differ substantially from another. RAID 3 and RAID 4 are often confused and even used interchangeably.
One of the early uses of RAID 0 and 1 was the Crosfield Electronics Studio 9500 page layout system based on the Python workstation. The Python workstation was a Crosfield managed international development using PERQ 3B electronics, benchMark Technology's Viper display system and Crosfield's own RAID and fibre-optic network controllers. RAID 0 was particularly important to these workstations as it dramatically sped up image manipulation for the pre-press markets. Volume production started in Peterborough, England in early 1987.
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