R.A.I.D.

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R.A.I.D.
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What is RAID?

• RAID stands for
• Redundant Array of Inexpensive Disks
• A RAID setup consists of two or more disks
  working in parallel.
• There are many different levels of RAID and they
  all have benefits and drawbacks.

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The Levels of RAID

• The levels of RAID are
• 0, 1, 3, 5, 50, 01, and JBOD.
• Note that there are other RAID levels
  (2,4,6,7,10) but are rarely used.

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What makes RAID possible?

• The thing that makes a RAID work is something
  called a RAID controller. (Controls the flow of
  data to the disks.)
• A RAID controller can be software emulated (which
  is cost effective but draws resources from the
  CPU slowing down the machine) or u can use other
  hardware to control RAID arrays.
• What is common in personal computers today is a
  hardware RAID controller.

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RAID controllers Cont.

• Because personal computers today use separate
  hardware to control the RAID arrays they see an
  increase in performance when using RAID arrays.
• In most laptops and desktops the RAID controller
  is either the South/Northbridge or a separate
  chipset.

-EPoXs EP-9NPA SLi Main board. With two RAID
controllers (Northbridge Sil 3132 chipset)
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RAID Level 0

• Known as striping the data blocks are fed to
  the RAID controller which splits the data up into
  parts of itself (depending on how many disks you
  have).
• Data block 1 becomes A,B,C, and D.
• RAID 0 requires at least two disks.

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RAID 0 Continued

• RAID 0 is not true RAID because there is no
  redundancy
• RAID 0 greatly improves disk performance .
  However, if one disk fails all of the data is
  lost.
• RAID 0 is good for any application that requires
  high bandwidth and no mission critical
  environments.

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RAID Level 1

• RAID 1 mirroring is when the data written on
  one disk is also written on another disk creating
  an on the fly backup.
• Performance is not very good but security is
  great.
• RAID 1 requires a minimum of two disks.

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RAID Level 3

• In RAID level 3 the data block sent to the disk
  is broken down and striped in x parts where x is
  the number of total disks in the array minus one.
• Each part of the data block is striped and sent
  to the different disk drives.
• The last unaccounted for disk is a parity disk
  where the is a parity written for each block of
  data that is striped to ensure security if one
  drive should fail.

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What is Parity?

• In RAID a parity, or parity bit, is a binary
  digit that indicates whether the number of 1 bits
  in the preceding data is even or add. If a bit
  is changed the parity bit will send out and error
  code and attempt to fix the changed bit.
• This gives the user of a RAID an on-the-fly way
  of error checking the disk.

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RAID 3 Continued

• In RAID 3 data rates are high and there is an
  added level of security RAID 0 doesnt offer.
• However, your RAID controller will be very
  complex.

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RAID Level 5

• RAID 5 is a disk array with a rotating parity
  array which makes the data array both safe while
  maintaining performance for Reading data but at
  average Write performance.
• A RAID 5 setup needs a minimum of 3 disks and
  most commonly uses 5 disks.

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RAID 5 Continued

• RAID 5 is used primarily for file and application
  servers, database servers, web, e-mail, and news
  servers.
• The RAID controller is the most complex for a
  RAID system
• Even though RAID 5 can have a disk failure it is
  difficult to rebuild from that failure (comparing
  to RAID 1).

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Other RAID Configurations

• RAID 50 is much like RAID 5 and RAID 0. There
  are two RAID 5 arrays (with rotation parities)
  and blocks or data are striped between the two
  like in a RAID 0 array. One disk failure is
  acceptable, two renders the array useless.

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Other RAID Configurations

• RAID 01 is exactly how it sounds. This array is
  a combination of RAID 0 and RAID 1 where data is
  stripped between drives and then the stripped
  array is mirrored basically creating two RAID 0
  arrays.
• Lastly RAID JBOD (Just a Bunch Of Disks) is just
  that, a bunch of disks strung together (end to
  end) in order to make a 2G 4G 10G and a 30G drive
  look like a 46G hard drive. (by definition this,
  just as RAID 0, is not really a RAID)

-This gives you both reliability and performance
but at a high cost. Byte/Byte cost is twice the
original cost.
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References

• http//www.acnc.com/04_00.html
• Advanced Computer Network Corporation