what exactly is raid?

[Advocation]

i have heard loads about it but am not 100% shure what it is and have been unable to find a decent guide..

my understanding of it is you have say for example three hard drives, when you write something to the first one then it copy's it to the second and then the third one copy's it from the second and so on,

is that correct?

also, what is the difference between raid 0, raid 1, raid 2 and any others there may be?!?

thanx

[ScYcS]

http://www.acnc.com/04_00.html

This should answer all your questions....if not, don't hesitate to ask further. There are books written about this topic, explaining it in one sentence is not going to cut it.

[Shakezilla]

That helped me a lot too thanks.

Can any HD be put in a RAID config? Or do you need a special one?

[ScYcS]

Any hd can be raided as far as i know. However, for a useful raid, the hdds should be the same kind (size, rpms, cache and manufacturer).

[defakto]

Quick run down of raid.

Redundant Array of Independant(or Inexpensive) Discs

these are the raid types i know of probably more
raid 0: striping, no data protection, data is striped on drives to read from all at once size = x(smallest drive size)
raid 1: Data is mirrored to (x) drives, where is x-1 fails you still have all your drives. Size = smallest drive size no matter how many discs are used
raid 3: minimum 3 drives, one drive is use for parity, the other drives are striped, if parity drive dies you can rebuild it, if one of the others die, you can rebuild that data(I believe, no experience with this one, correct me if i'm wrong. I'm doing this all off the top of my head.) size is (x-1)(size of smallest)
raid 5: minimum 3 drives, rotating parity, size of array is equal to (x-1)size of smallest drive. Parity info is rotated across drives during the write process so no single drive contains all parity info
raid 6: Just heard of a card that does this one the other day. Requires minimum of 4 drivers, size of array is (x-2)size, uses rotating partiy like raid 5 but writes 2 sets instead of one.
raid 10: minimum 4 drives, size is (x/2)(size of smallest), must be even number of drives. combination of raid 0 and raid 1
raid 50: minimum 6 drives, size is (x-2)(size of smallest), combination of rand 5 and 0

There are other types but they are less commonly used from my experience but they are used for some applications.

Please if I got something wrong let me know so I can update my brain.

[Falls Included]

any 2 hard drives can be put into a raid array, but the array will only run as fast as the slowest hard drive...

and the capacity will vary, i'd suggest 2 drives that are the same brand, speed and size, and not using raid 0 unless you use it for not crital data, or anything you can afford to loose

[defakto]

Some types of raid require more than 2 drives and array speed will not be equal to the slowest drive. It will vary in speed by how many drives you have in it and what type of raid you are using. That is a worst case scenario with a 2 drive raid 1 for speed.