Netsted RAID Confusion

Is it RAID 0+1 or 1+0?

I see this happen quite often when it comes to nested RAID arrays. Manufacturers of RAID systems don’t help much as they quite often mix things up too. This usually comes up when comparing performance or fault tolerance of RAID 5 or 6 to RAID 10. The proponents of RAID 5 or 6 will typically, and many times unknowingly, substitute RAID 0+1 for 10. When it comes to nested RAID arrays the first number is applied first when building the array. The second number is then applied to the existing arrays. Assuming 6 disks for simplicity a RAID 0+1 would start out with 2 RAID 0 arrays with 3 disks in each array. Then the two RAID 0 arrays would be mirrored in a single RAID 1 array.

A RAID 10 (1+0) array starts by creating three RAID 1 arrays (2 disks in each array) and then striping them into a single RAID 0 array.

So what’s the difference?