RAID History and Alternatives
Before RAID devices became popular, most systems used a single drive to store data. This arrangement is sometimes referred to as a single large expensive disk or SLED. However, SLEDs have some drawbacks. First, they can create I/O bottlenecks because the data cannot be read from the disk quickly enough to keep up with the other components in a system, particularly the processor. Second, if a SLED fails, all the data is lost unless it has been recently backed up onto another disk or tape.
In 1987, three University of California, Berkeley, researchers -- David Patterson, Garth A. Gibson, and Randy Katz -- first defined the term RAID in a paper titled A Case for Redundant Arrays of Inexpensive Disks (RAID). They theorized that spreading data across multiple drives could improve system performance, lower costs and reduce power consumption while avoiding the potential reliability problems inherent in using inexpensive, and less reliable, disks. The paper also described the five original RAID levels.
Today, RAID technology is nearly ubiquitous among enterprise storage devices and is also found in many high-capacity consumer storage devices. However, some non-RAID storage options do exist. One alternative is JBOD, short for "Just a Bunch of Drives." JBOD architecture utilizes multiple disks, but each disk in the device is addressed separately. JBOD provides increased storage capacity versus a single disk, but doesn't offer the same fault tolerance and performance benefits as RAID devices.
Another RAID alternative is concatenation or spanning. This is the practice of combining multiple disk drives so that they appear to be a single drive. Spanning increases the storage capacity of a drive; however, as with JBOD, spanning does not provide reliability or speed benefits.
RAID should not be confused with data backup. Although some RAID levels do provide redundancy, experts advise utilizing a separate storage system for backup and disaster recovery purposes.