RAID is storing your information in multiple disk drives but they are treated as one by the computer. By spreading out the stored information, you will capacity, speed, and reliability in different ways. In my post I will briefly give an introduction and describe the four most common RAIDs, RAID 1, RAID 0, RAID 5, & RAID 6.
RAID 1 - Mirroring
RAID 1 uses two disk drives and creates two identical copy the data, hence the name mirroring. Everything that the computer stores RAID 1 will send the information to both hard drive A and hard drive B. Consequently if for some reason one hard drive A fails, hard drive B will still have all your information safe. Not only will your information still be safe but your computer does not slow down if a hard drive fails it will continue to run at full speed. Even though you as the user will probably not notice the difference if a hard drive fails, it is important to have a hot spare disk. After replacing the dead hard drive A with the hot spare, hard drive B will mirror all the information it has to hot spare and it will be back to normal. The only con is that RAID 1 is pricey.
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| Attached diagram demonstrates how the Raid 0 distributes file 1, 2, & 3. |
RAID 0 - Striping
Raid 0 is used with two or more disk. The more disk that are in use the faster it will run. What RAID 0 does it distributes the data evenly between the disks in use, that it is why RAID 0 is also known as Striping. By spreading out the information through different hard drives you gain a lot of speed. This is ideal for simultaneously working on both read and write request. Sadly all is not good, thou being the fastest it is also the least dependable. If one hard drive fails the entire system will fail, crash, and all data will be lost. It is known that RAID 0 is actually least dependable then just having a stock normal one hard drive you get from a thick client.
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| Attached diagram displays how RAID 0 spreads out its stored information |
RAID 5
Raid 5 uses three or more hard drives and RAID 5 hardware to store information. Information is stored in all disk excluding one. For example lets say you are have three hard drives A, B, & C. Hard drive A & B will be used to store information, while hard drive C will be doing something called parity. Parity calculates and then stores information on the remaining unused drive. But don't get int confused there is no certain parity drive. For example same scenario we have the same three hard drives but now we want to store a new file. Now hard drive A & C will be in use to store information, while hard drive B is calculating the parity. By doing this your performance increase drastically, information is read faster, and write speed is common. If a hard drive fails with RAID 5 no data will be lost. The system will still be up and running, but unlike mirroring you will loose performance. With RAID 5 you can substitute a dead disk with the hot spare that I discussed earlier. After the process of reconstruction the data on the new disk performance will be back to normal. RAID 5 is commonly found in network servers everywhere.
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| Attached diagram displays how RAID 5 creates its parity code to save data |
RAID 6
RAID 6 extends RAID 5 by adding an additional parity block. So if you have four disk drives in use when it comes to storing information only two will actually store information, while the other two are calculating the parity. The reason why this is used is because it protects against read failures during rebuild of a large hard disk which will usually result in loss of massive amount of data. Performance wise it runs like RAID 5 it reads fast but writes slow and also needs hard ware to support it.
(There is no diagram for RAID 6, due to the similarities that it has with RAID 5)
Just like everything else when it comes to choosing which RAID is right for you, you must due an analysis and see what your trying to get out of the RAID. For the normal PC user I strongly recommend for you to USE RAID 1.
REFERENCES:
http://en.wikipedia.org/wiki/Raid_0#RAID_0
http://www.ehow.com/facts_5148033_computer-raid.html
All photos have been made in Microsoft Paint, and created by Dario Gonzalez II
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