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Confused Raid settings

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March 2, 2011 4:24:27 PM

I have been looking into setting up a raid for a little fileshare server I have. I can get 3-5 hdd's. I am looking for performance and protection from 1 harddrive failure (not complete mirror of everydrive). this rules out raid 0,1,10

I imagine it was either raid 3-4-5 not sure which one though?

any assistance would be appreciated

More about : confused raid settings

a c 289 G Storage
March 2, 2011 5:45:37 PM

Well, RAID 1+0 uses four drives and completely protects you from one hard drive failing. Have you read a tutorial on the way that various RAID levels work?

If I, personally, were going to RAID, I would start with a RAID 1+0.

Please keep in mind that RAID is not a substitute for backups. It leaves you vulnerable to many kinds of failures. A controller failure may leave you with disks that are useless unless you have a spare of the same kind of controller.

To get the most capacity out of what disks you have, RAID 5 is in order, since you have the capacity of all but one of the drives in the array. Raid 1+0 only gives you the capacity of half the drives in the array.

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What to do depends on what you want to use this for. If it's a "little" fileshare server, RAID 0 in software may be good enough for you. Depends on how little. If you are going to share 500GB of data and have two 1TB drives in RAID0, then you are set. A little-to-never used configuration is more than two drives in RAID0 for low-write, high-read environments. Spread the reads across multiple platters!

If you want to play around and learn, then the sky is the limit.
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March 2, 2011 6:12:51 PM

Thanks, I quite enjoy well thought out positive answers. I have wiki'd and check some forums on the difference of RAID levels however I got lost with the word parity. would you be able to link any possible guides or tutorials?

I am very capable on a computer, just never dabbled in RAID

My usage is a Media PC that double as a NAS. It'll be running with 2gb/s full duplex link aggregation. I was looking at 4x 2tb drives. hopping to net atleast 5tb storage with protection against a single drive pooping the bed. hot swapable kind of thing, minus the word hot....
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a c 289 G Storage
March 2, 2011 7:18:12 PM

Well, that makes RAID level selection easy. The best way to get 5 GB (actually, 6) out of 4x 2TB drives with protection against a single drive failure is RAID 5. 3 and 4 are candidates, but they are not often used because 5 works better.

If one drive fouls the sheets, your array will be "degraded." When you put in a new, blank drive, the RAID array will spend many hours "rebuilding" and then be a good RAID5 again. No, I don't know the instructions for accomplishing this with your particular setup.

Parity: "A literary or artistic work that imitates the characteristic style of an author or a work for comic effect or ridicule." Oh, wait, someone else has the Forum Jester title.

Parity is a relatively simple way to recover from the loss of one bit / byte / block out of a set of N. I will illustrate the trivial case of three data bits and one parity bit.

Data Parity Bit
000 0
001 1
010 1
011 0
100 1
101 0
110 0
111 1

Let's say you send me the message 100 110 111. You add parity and send me 1000 1100 1111. I lose two bits, and get the message 10x0 1100 1x11. It's easy for me to figure out that the missing bits were 0 and 1, looking at the overall parity (number of ones) in each overlong "word."

How does this apply to storage? Conceptually, in RAID5, you store one bit of each three-bit word on a separate drive, and the parity on a parity drive. Which drive is the parity drive alternated between three-bit words.
If any one drive dies, I can easily 1) Reconstruct what the message was for any given 3-bit word, and 2) Reconstruct the drive that died from the other three.
In reality, parity is not done at the bit level, but the block level, and block size can be configured.


(Yes, all of you out there, I know that a flipped parity bit will be better, so that there are always an odd number of ones. I'm being incredibly simplistic.)

Edit: Hah! I figured the parity wrong in my example message! :??: 
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March 2, 2011 7:37:44 PM

Best answer selected by jonnyrb.
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