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What are the different widely used RAID levels and when should I consider them?

I haven't had any trouble building mental images of the simpler RAID forms, but for some reason my head spins when I try to think about 10. Let me walk through my conception:

Mirroring is obvious: N drives, each with a copy of the same data X. So for N=2, we have D(isc) 0 with Xcopy0, and D1 with Xcopy1.

Striping is obvious: N drives, each with 1/Nth of each byte. So for N=2, we have D(isc)0 with Stripe0 having every nybble 0, and D1 with Stripe1 having every nybble 1.

For 10, let's say with 2-bit stripes (i.e., 4 discs), do we need 8 discs, where we mirror D0+D4, D1+D5, D2+D6, and D3+D7, and then stripe D0..D3 (and D4..D7, or does that come for free?).

Or does it work some other way?

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MMacD
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1 Answers1

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Raid 10 is pretty easy. It is a combnination of mirroring (Raid 1) and striping(Raid 0). Instead of striping over single disks you strip over a set of mirrored disks. 

 Mirror1            Mirror2
+-------+          +-------+
| disk1 | Striping | disk3 |
+-------+ -------- +-------+ -----...
| disk2 |          | disk4 |
+-------+          +-------+

This enhances write performance, read performance and redunancy.

You can add as many mirrors as you want to stripe over as many mirror blocks as you want.

Christopher Perrin
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