RAID 6

Wikipedia defines raid as "...an umbrella term for data storage schemes that divide and/or replicate data among multiple hard drives..."

So that is pretty self explanatory in what RAID is used for. You can choose from 6 different type of RAID schemes.

[b]Q.[/b] [u]How many drives do into a raid group?[/u]
[b]A:[/b] Different RAID require different number of disks. Below is a brief list with the number of disk required for each RAID:

RAID 0: minimum 2 disks
RAID 1: mirrored set (minimum 2 disks) without parity
RAID 3 and RAID 4: striped set (minimum 3 disks) with dedicated parity
RAID 5: striped set (minimum 3 disks) with distributed parity
RAID 6: striped set (minimum 4 disks) with dual distributed parity

[b]Q.[/b] [u]Why would you have different raid groups vs one raid group?[/u]
[b]A:[/b] All RAIDs' are unique in some sense. They provide the basic function of data loss prevention and or improved performance. However depending on you needs, you can implement any of the 6 type. I can't explain all of them here but there's a link for it at the bottom.

[b]Q.[/b] [u]Is a raid group presented as C: in windows?[/u]
[b]A:[/b]
No probably not as C:, but it can be explored. Your can access it the same way you would a secondary hard drive.

Read this article for your knowledge:
http://en.wikipedia.org/wiki/RAID

Hope this answer helped.

Ash

It sounds to me like you're just a bit confused on how RAID works:) Let me see if I can break it down for you.

Your first question is how many drives are in a raid group. The truth is that it depends on which RAID type you go for. RAID is Redundant Array of Independent [or Inexpensive] Disks. Each RAID level produces a different arrangement of your hard drives. For example, RAID 0, Striped, causes two drives to act as one big drive that Windows can write data to. It writes data to one "stripe" or part of your drive, and then writes it onto the other "stripe" on a second drive, and goes back and forth between writing to the two drives. This allows for MUCH faster access times to your drives. BUT, keep in mind, if one of those drives dies, all your data is lost, because you only have half of all your files.

Then there's RAID 1, mirrored. RAID 1 causes two drives to look identical. This type of array is good for a desktop redundancy system so you can install 2 drives of the same size, let's say, 2 250GB drives, and still have a total of 250GB's, because whatever the computer writes to one drive, it writes to the other. So they're exact copies of each other, so if one fails, the other one picks up, and your system doesn't stop running. It will just tell you on your next boot you have one dead drive in your array and you should replace it as soon as possible to get your redundancy back up.

Then there's really nice arrays like RAID 10, which is one of my personal favorites as well as RAID 5. RAID 10, uses Striping AND Mirroring. You need a minimum of 4 drives in the array, 2 stripe each other for high speed access, and the other 2, mirror the first two which are striping. This means you're getting that really fast performance I talked about earlier, and at the same time, it's all being copied to a second array of disks! Now you don't have to worry if one stripped drive dies. Really nice setup for servers.

Another thing that's really nice is let's say a drive dies in the RAID array. What happens? You simply just have to replace it if it's mirrored. Just pop in another drive, and on the others [depending on your hardware setup] should recognize the new drive, and automatically restore it to the way the dead one was, "catching" the drive up to where the active one is.

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Your second question was why would you have different RAID groups. I think I've mainly explained that. There are so many different options you can have. But video editing for example, I like to have a RAID array with striping for fast access to video files and rendering, and I like to have a redundant backup incase all that work goes corrupt on one drive if the drive dies.

Servers I'd use the same kind of array, and desktops I'd use just a simple RAID 1 mirror.
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The last question was is a RAID group presented as C: in windows. Yes, usually it is. Although drive letters of course can change and you can add any drive letter to a RAID array you like. But yes, if you have a RAID 1 array in a desktop for example, the two mirrored drives will show up as one drive C: [if c is your main system drive.

Hope that helps!

For more information see one of my favorite sites for RAID:
http://www.acnc.com/raid.html