Different Types of RAID
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[Synopsis]
This video describes the various types of RAID configurations. It is important to know if you plan to use RAID on computers, workstations, and servers. Different types of RAID have different requirements, like the number of storage devices which are required to use that configuration.
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[Definitions]
♦ RAID ► It stands for Redundancy Array of Inexpensive Disk or Redundancy Array of Independent
Disks. RAID is a data storage virtualization technology that combines two or more storage
devices into one or many logical units. This is done to provide redundancy to safe guard
your data, or to improve the performance of your storage devices.
♦ Parity ► Parity is used in RAID arrays to provide fault tolerances by calculating the data in two
drives and storing it in a 3rd drive. It uses XOR which is a Boolean operator in math.
XOR is the opposite of OR.
A | B OR A | B XOR
1 1 1 1 1 0
1 0 1 1 0 1
0 1 1 0 1 1
0 0 0 0 0 0
For or, true and true is true, true and false is true, false and true is true, and false + false
is false. For xor, true + true is false, true + false is true, false + true is true, and false +
false is false. Since two drives are storing parity in the 3rd drive, and one drive fails.
True or False is True, and False or True is True. If both drives fail, true and true is false.
♦ Parity Calculations ► Using 4 sets of 4 bits for 4 drives.
Disk 1 = 1111
Disk 2 = 1110
Disk 3 = 1100
Disk 4 = 1000
(1111) XOR (1110) XOR (1100) XOR (1000)
(1111 XOR 1110) = 0001
(0001) XOR (1100) = 1101
(1101) XOR (1000) = 0101
♦ Fault Tolerance for RAID ► Raid 3 One drive can fail
Raid 4 One Drive failure
Raid 5 One Drive can fail
Raid 6 Two drives can fail
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