RAID Technology

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RAID Technology
By Chuck Barbeau
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What is RAID?

• Redundant Array of Independent Disks
• RAID is a great system for increasing speed and
  availability of data.
• Used for Data Protection

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Timeline of RAID Technology

• 1956 IBM officially announces the RAMAC 305, the
  first hard disk system, which holds 5MB of data.
• 1961 Ampex develops helical scanning video
  recording, which will later be adapted for
  high-capacity tape backup.
• 1973 IBMs sealed Winchester hard disks become
  the standard design for disk drives.
• 1979 Al Shugart and Finis Conner launch Seagate
  Technology to produce hard disk drives for
  desktop computers.
• 1988 David A. Patterson leads a team that
  defines RAID standards for improved performance,
  reliability and scalability.

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Timeline of RAID Technology

• 1956 IBM officially announces the RAMAC 305, the
  first hard disk system, which holds 5MB of data.
• 1961 Ampex develops helical scanning video
  recording, which will later be adapted for
  high-capacity tape backup.
• 1973 IBMs sealed Winchester hard disks become
  the standard design for disk drives.
• 1979 Al Shugart and Finis Conner launch Seagate
  Technology to produce hard disk drives for
  desktop computers.
• 1988 David A. Patterson leads a team that
  defines RAID standards for improved performance,
  reliability and scalability.

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Advantages of RAID

• Affordable alternative to mass storage
• Cost/Megabyte is dropping.
• Smaller drives make this possible.
• High output and reliability
• High I/O rates, less power/megabyte.

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Why Use RAID?

• RAID devices can act as a single drive.
• Allows simultaneous read/write.
• Overall increase in I/O performance.
• Provides data redundancy.

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RAID Level 0Striping
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Advantages Disadvantages

• Advantages
• RAID 0 offers great performance, both in read and
  write operations.
• All storage capacity is used, there is no disk
  overhead.
• The technology is easy to implement.
• Disadvantages
• RAID 0 is not fault-tolerant. If one disk fails,
  all data in the RAID 0 array are lost. It should
  not be used on critical systems.

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RAID Level 1Mirrored
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Advantages Disadvantages

• Advantages
• RAID 1 offers excellent read speed and a
  write-speed that is comparable to that of a
  single disk.
• In case a disk fails, data do not have to be
  rebuild, they just have to be copied to the
  replacement disk.
• RAID 1 is a very simple technology.
• Disadvantages
• The main disadvantage is that the effective
  storage capacity is only half of the total disk
  capacity because all data get written twice.

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RAID Level 3Byte level Striping Parity
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Advantages Disadvantages

• Advantages
• RAID-3 provides high throughput (both read and
  write) for large data transfers.
• Disk failures do not significantly slow down
  throughput.
• Disadvantages
• This technology is fairly complex and too
  resource intensive to be done in software.
• Performance is slower for random, small I/O
  operations.

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RAID Level 5Block Level Striping with Parity
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Advantages Disadvantages

• Advantages
• Read data transactions are very fast while write
  data transaction are somewhat slower (due to the
  parity that has to be calculated).
• Disadvantages
• Disk failures have an effect on throughput,
  although this is still acceptable.
• Like RAID 3, this is complex technology.

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RAID 10 RAID 0 RAID 1
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RAID 10 Very High Reliability combined with High
Performance

• Characteristics/Advantages
• RAID 10 is implemented as a striped array whose
  segments are RAID 1 arrays
• RAID 10 has the same fault tolerance as RAID
  level 1
• High I/O rates are achieved by striping RAID 1
  segments
• Under certain circumstances, RAID 10 array can
  sustain multiple simultaneous drive failures
• Excellent solution for sites who would have
  otherwise gone with RAID 1 but need some
  additional performance boost

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Disadvantages

• Very expensive / High overhead
• All drives must move in parallel to proper track
  lowering sustained performance
• Very limited scalability at a very high inherent
  cost

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JBOD Just a Bunch of Disks (drives)

• Tacks one disk onto the end of another without
  striping. There's minimal performance
  improvement, the only significant gain is that
  you have one big volume instead of a bunch of
  little ones.

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RAID Manufacturers

• Comix International
• Sea Storage
• Norco

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Sources

• http//en.wikipedia.org/wiki/RAID
• http//www.webopedia.com/TERM/R/RAID.html
• http//www.computerworld.com/s/article/87093/The_S
  tory_So_Far
• http//www.prepressure.com/library/technology/raid