RAID 0, RAID 1, RAID 5, RAID 10 with Diagrams

RAID stands for Redundant Array of Independent Disks,originally Redundant Array of Inexpensive Disks.

On most situations you will be using one of the following four levels of RAIDs.

  • RAID 0
  • RAID 1
  • RAID 5
  • RAID 10 (also known as RAID 1+0)

This article explains the main difference between these raid levels along with an easy to understand diagram. In all the diagrams mentioned below:

  • A, B, C, D, E and F – represents blocks
  • p1, p2, and p3 – represents parity
RAID LEVEL 0


Following are the key points to remember for RAID level 0.

  • Minimum 2 disks.
  • Excellent performance ( as blocks are striped ).
  • No redundancy ( no mirror, no parity ).
  • Don’t use this for any critical system.
RAID LEVEL 1

Following are the key points to remember for RAID level 1.

  • Minimum 2 disks.
  • Good performance ( no striping. no parity ).
  • Excellent redundancy ( as blocks are mirrored ).
RAID LEVEL 5


Following are the key points to remember for RAID level 5.

  • Minimum 3 disks.
  • Good performance ( as blocks are striped ).
  • Good redundancy ( distributed parity ).
  • Best cost effective option providing both performance and redundancy. Use this for DB that is heavily read oriented. Write operations will be slow.
RAID LEVEL 10

Following are the key points to remember for RAID level 10.

  • Minimum 4 disks.
  • This is also called as “stripe of mirrors”
  • Excellent redundancy ( as blocks are mirrored )
  • Excellent performance ( as blocks are striped )
  • If you can afford the dollar, this is the BEST option for any mission critical applications (especially databases).
Comparison

The following table provides an overview of some considerations for standard RAID levels. In each case:

  • Array space efficiency is given as an expression in terms of the number of drives, n; this expression designates a fractional value between zero and one, representing the fraction of the sum of the drives’ capacities that is available for use. For example, if three drives are arranged in RAID 3, this gives an array space efficiency of 1 - (1/n) = 1 - (1/3) = 2/3 \approx 67%thus, if each drive in this example has a capacity of 250 GB, then the array has a total capacity of 750 GB but the capacity that is usable for data storage is only 500 GB.
  • Array failure rate is given as an expression in terms of the number of drives, n, and the drive failure rate, r (which is assumed to be identical and independent for each drive). For example, if each of three drives has a failure rate of 5% over the next three years, and these drives are arranged in RAID 3, then this gives an array failure rate of 1-(1-r)^{(n-2)/2} = 1-(1-5%)^{(3-2)/2} = 1-(0.95)^{(1)/2} = 1-(0.95)^{(0.5)} \approx 1-(0.975) \approx 0.025 \approx 2.5% over the next 3 years.
Level Description Minimum # of drives** Space efficiency Fault tolerance Array failure rate*** Read performance Write performance Figure
RAID 0 Block-level stripingwithout 
parity or
mirroring
2 1 0 (none) 1−(1−r)n nX nX RAID Level 0
RAID 1 Mirroring without parity or striping 2 1/n n−1 drives rn nX***** 1X RAID Level 1
RAID 2 Bit-level striping with dedicated 
Hamming-code parity
3 1 − 1/n ⋅ log2(n-1) RAID 2 can recover from one drive failure or repair corrupt data or parity when a corrupted bit’s corresponding data and parity are good. Variable Variable Variable RAID Level 2
RAID 3 Byte-level striping with dedicated parity 3 1 − 1/n 1 drive 1-(1-r)(n-2)/2 (n−1)X (n−1)X* RAID Level 3
RAID 4 Block-level striping with dedicated
parity
3 1 − 1/n 1 drive 1-(1-r)(n-2)/2 (n−1)X (n−1)X* RAID Level 4
RAID 5 Block-level striping with distributed parity 3 1 − 1/n 1 drive 1-(1-r)(n-2)/2 (n−1)X* (n−1)X* RAID Level 5
RAID 6 Block-level striping with double distributed parity 4 1 − 2/n 2 drives 1-(1-r)(n-3)/2 (n−2)X* (n−2)X* RAID Level 6
RAID 10 Mirroring without parity, and block-level striping 4 2/n 1 drive / span **** nX (n/2)X
Level Description Minimum # of drives** Space efficiency Fault tolerance Array failure rate*** Read performance Write performance Figure

More Ref http://en.wikipedia.org/wiki/RAID. Try

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