Operating Systems/Programming

RAID Information

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Raid Definition

  • A RAID, (redundant array of independent disks) is a disk subsystem that combines multiple physical disk drives into a single logical unit and either provides fault tolerance, increases performance or both
  • RAID can be either software or hardware based
  • Capacity is calculated by the number of Drives x Capacity of Disk = Capacity of Array

History of raid

In 1978, Norman Ken Ouchi at IBM was awarded U.S. Patent 4,092,732 which was titled “System for recovering data stored in the failed memory unit.”

In 1987, levels 1-5 of RAID were formally designed by David. A. Patterson, Garth A. Gibson, and Randy H. Katz

Raid information

  • Early disk drives were expensive, large, and needed strict environmental control
  • RAID is the idea of linking up a bunch of smaller and cheaper disks, together
  • There are numerous types of RAID methods however RAID Levels 0-10 will be discussed

RAID Level 0

  • Implements data stripping but no redundancy of data
  • Most affordable option and offers fast speeds
  • No-fault tolerance
  • No parity calculation is involved

Raid Level 1

  • Implements data mirroring, consists of at least two drives that duplicate the data storage
  • Great protection against crashes
  • Provides the best performance and the best fault-tolerance in a multi-user system

Raid Level 2

  • Implements bit stripping with error checking information (ECC)
  • Fast read-and-write abilities, high protection
  • Slow hamming code generation, low commercial use, expensive

Raid Level 3

  • Implements bit striping and dedicates one drive to storing parity information
  • Embedded (ECC), enhanced data recovery
  • Ideal for single-user systems with long record applications

Raid Level 4

  • Implements block-level data striping with parity data on a single disk
  • High performing random reads
  • Low performing random writes

Raid Level 5

  • Implements block-level striping with distributed parity
  • Parity information is distributed among the drives and requires all to be present
  • Cost effective. Most complex design

Raid Level 6

  • Implements data stripping with dual error protection
  • Can continue to read-and-write requests to all of the virtual disks in the presence on 2 concurrent disk failures
  • Complex to set-up

Raid Level 10

  • Combination of RAID 0 and RAID 1 in a single system
  • Hybrid/Nested RAID configuration
  • Uses 2 disks which allow the system to always be backed-up and easily fixed if a single disk malfunctions

 

References

http://www.pcmag.com/article2/0,2817,2370235,00.asp

“RAID Levels Explained.” Samara Lynn. PCMag. Pcmag.com. Web. 27 March 2014. Retrieved 4 July 2017.

http://www.raid-calculator.com/raid-types-reference.aspx

“Raid-Calculator.com.” ReclaiMe Team. ReclaiMe.com. Web. Retrieved 4 July 2017.

 

 

 

 

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