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A lot of people become confused by this because they usually only think of a RAID array as containing a small number of drives. For example, RAID0 or RAID1 arrays are usually built using two drives, no more. However, consider a system using 8 drives for a RAID array. We are after redundancy here, because it's a RAID array after all, and RAID5 is too slow for what we want to do, plus drives are cheap these days, 8 drives, no problem. So we're going to make a RAID array that consists of mirroring and striping. Our newbie tech guys things, RAID0+1, no problem, solves all our worries.

In this configuration of drives we have the following
M I R R O R
Array1 => Array2 = Drive
RAID 0 + RAID0 = RAID0+1
S
T 1 5
R 2 6
I 3 7
P 4 8
E
Two separate striped arrays of 4 drives each, mirrored, RAID0+1. Okay, consider, our techie is feeling pretty smug about his data all nice and safe except 6pm Firday evening, drive 3 decides to go down. Now what do we have?

DOWN + RAID0 = RAID0
1 5
2 6
(3) 7
4 8

A non-functional RAID0 array and it's mirror, RAID0 array 2. So now all our mission critical data is stored on a RAID0 array!!! That's BAAAD, suddenly what our techie thought was a nice secure RAID0+1 array has become a super scary RAID0 array. Unfortunately for our techie the RAID0+1 arrray is situated offsite and he can't get to it until Monday morning. In the meantime, disaster strikes and drive 5 in array 2 decides to go down. End of array!! Data lots, customers pissed etc.

So why does our techie wish he'd made a RAID10 array? Take a look, same situation, drive 3 and 5 have done down, but look the array is still functioning perfectly.

MIRROR S
Array1 RAID1 1 => (5) T
Array2 RAID1 2 => 6 R = DRIVE
Array3 RAID1 (3) => 7 I
Array4 RAID1 4 => 8 P
E

Although there's no difference between RAID0+1 and RAID10 with regard to the data on the drives, that is, in the RAID0+1 array the data on drives 1 and 5 is exactly the same as the data in the RAID10 array, the essential difference is the way in which the controller access the data. Because a RAID0+1 array consists of two RAID0 sub-arrays the controller only sees the two separate sub-arrays, it isn't set up to read between them (then it would be RAID10), hence it only requires one drive in each of those sub-arrays to go down to cause the whole array to fail. In a RAID10 array you need two drives in the same mirror sub-array to go down. If you do the math you'll realize that, particularly as array size increases, the chances of a RAID0+1 array failing increase with the more drives you add, whereas the chances of a RAID10 array actually decrease (given that there is no measure for the chance of a particular drive failing, drive failures are reported in MTBF for groups of drives).

Hope that makes sense.

In addition to the point made above, that RAID 10 can handle more failure modes than RAID 0+1 can, there is another important difference: When a bad drive is replaced in a RAID 10, there are only 2 drives involved in the rebuild - the working drive of the mirror and the new drive. With a RAID 0+1, once a drive is replaced, all 8 drives in the array are involved in the rebuild. This increases the chance that the array may suffer another failure before the rebuild completes, which will lose all data.

RAID 10 is generally always the best choice for a RAID 0/RAID 1 nested combination. One problem that you run into is that many motherboard-based and software/firmware-based RAID solutions implement only RAID 0+1 as their nested level. Some even go so far as to claim they do RAID 10, when they're really doing RAID 0+1.

Query: I am trying to set up RAID0 on XP Pro64 (already installed). Although I can not see the second SATA in "My Computer", I have, nevertheless, gone into disk management and converted both to "dynamic". My problem is that, when I go in to add a new volume/striped, the new volume wizard will only allow me to select "simple"... Striped and Spanned are grey'd out. Any thoughts?

What software can be used to create a USB RAID 1 mirroring hard drive for a laptop? Unlike a desktop, laptops often don't have the hardware capability for two HD RAID 1.

I have two disk used to set as Raid 0, and another disk as ACHI . I accidentally set them as Raid 5, and created a 50G partition. After that, I realized that my third disk became a member of Raid 5. Is there any way I can undo and get my data back from my third disk?

Gigabyte P35-D3R
Intel Sata controller

thanks

lol i have a feeling thats copied and pasted from the wiki article...

Great guide, but I have one question.

If Windows (Vista, in my case) is already installed, can one then set up a RAID without reinstalling the OS? It seems that you wouldn't be able to because it would have to stripe all of the data. Clean installs of Vista are always good but less so if you cheaped out and got the OEM.

I have a question:
I have a 250gb WD right now, I am buying 3 more 250gb's to set up RAID 0+1.
I have backed up everything with Acronis TrueImage 11. Can I just back it up with that because it saves the entire drive, or do I have to reinstall Vista because of the RAID