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RAID Basics

What is RAID?

Depending on who you ask, RAID either stands for Redundant Array of Inexpensive Disks, or Redundant Array of Independent Disks.

Hard drives are cheaper than everAdherents to the former school of thought, point out (and quite rightly too) that the word "Inexpensive" was used by the scientists at the University of California at Berkeley who first conceived of RAID. Detractors however, note that hard drives are anything but "Inexpensive," and that "Independent," would have been a more apt term.

Whatever the acrimony over acronyms, the original meaning of RAID seems much more appropriate today than it did in 1987 when Patterson, Gibson, and Katz published a paper entitled, "A Case for Redundant Arrays of Inexpensive Disks." Hard drives after all, are cheaper than ever before, offering gargantuan storage capacities at relatively low prices.

Research on RAID

Researchers came up with the idea of RAID while looking for ways to improve hard drive storage reliability and performance. The concept initially consisted of clustering small, "inexpensive" disk drives together into an array so that the array would appear to the system as a single logical drive.

During initial testing, it was discovered that an array of drives could actually deliver performance exceeding that of single, more expensive hard drives.

There was just one problem however -- a problem which underscores the importance of RAID data recovery. The Mean Time Before Failure (the average time before a failure will occur) in a RAID, was reduced due to the probability of any one drive in the array failing. Consequently, researchers proposed five levels of RAID to provide a balance between performance and data protection.

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