What is RAID

• "A Case for Redundant Arrays of Inexpensive Disks (RAID)", Patterson, Gibson and Katz (University of California Berkeley, 1987),  http://sunsite.berkeley.edu/TechRepPages/CSD-87-391.
• The basic idea of RAID was to combine multiple small, inexpensive disk drives into an array of disk drives which yields performance exceeding that of a Single Large Expensive Drive (SLED).
• Redundancy was introduced to prevent dramatic reduction of the Mean Time Between Failure (MTBF): without redundancy, failure of one disk leads to failure of the entire array.
• Five types of RAID were defined (RAID-0 and linear RAID were added later).
• Traditional advantages of RAID (viewpoint of an enterprise user):
• lower latency and/or higher bandwidth
• fault-tolerance for high uptime and reliability, for prevention of downtime, not for prevention of data loss
• fault-tolerance is not considered the main advantage, not a substitute for backups
• Viewpoint of Linux home user:
• fault-tolerance is the main advantage
• uptime is not a concern, data loss is, frequent backups are difficult
• high performance rarely matters
• combining multiple disks into one filesystem is convenient
• Different aspects of fault tolerance.