Re: Are RAID 1+0 and 10 the same thing?

Eduard:

As Gaja points out, most of the implementations are vendor specific and the term is used quite interchangably most of the time. From a purist's perspective, however, there are some subtle differences. This amounts to splitting hairs, but just for the sake of discussion, in RAID1+0 the disks are mirrored first and then striped; in RAID0+1 implementations the disks are first striped and then mirrored.

For the most part, this is more of an issue of fault tolerance than anything else. Follow me with a ten disk example (X1 - X5 and Z1 - Z5):

    X1 Z1

    X2 Z2

    X3 Z3

    X4 Z4

    X5 Z5

If we chose RAID0+1, then we would create a striped volume on X1 - X5 and on Z1 - Z5. Each of these striped volumes would be seen as a virtual disk and then those two striped disks would be mirrored (often this is done at the hardware level, though it can be done through software VM's as well). Now, in the event of a failure for a normal RAID0 set we know that because of the way that the data is laid out the RAID0 set cannot lose a single disk without losing the entire stripe. The striping is done to achieve higher I/O rates, but at the cost of increased likelihood of failure (it is more likely that 1 disk out of 5 will fail than 1 disk out of 1). By mirroring, we insure that if we lose a disk in our first stripe, everything is still mirrored on the second stripe and progress will go on unabated. However, if we were to somehow lose a disk on the first stripe and the second stripe then we would lose all of the data on this RAID0+1 disk and be forced into a recovery. It does not happen often, but it does happen.

In RAID1+0, the difference is that each of the individual disks are mirrored first (X1 & Z1, X2 & Z2, X3 & Z3, X4 & Z4, X5 & Z5) and then those disks are seen as virtual disks. Those mirrored virtual disks are then setup as one striped volume. Like RAID0+1, this can be hardware or software driven. In any event, the difference is that in order for us to lose data we would have to lose both sides of the mirror on an individual disk mirror (for example, X3 & Z3). In fact, we could lose all of the disks Z1 - Z5 and the data would still be accessible because of X1 - X5. This is because it is a stripe of mirrors vs. a mirror of stripes. As I mentioned before, this is really splitting hairs and this is only a purist's perspective.

Again, these terms are used pretty interchangably and you should ask the vendor for more specific details on what that means to them. I agree with Gaja that vendors will implement these differently.

"Shevtsov, Eduard" wrote:

> Hi List,
>
> is there any difference between 1+0 and 10?
>
> Regards,
> Ed
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> Please see the official ORACLE-L FAQ: http://www.orafaq.com
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> Author: Shevtsov, Eduard
> INET: EShevtsov_at_flagship.ru
>
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====================================================================
Byron Pearce                         mailto:bpearce_at_tenure.com
Tenure Systems, Inc.                 Arlington, Texas

"It's hard to be a ninja when you wear a beeper."


-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
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Author: Byron Pearce
  INET: bpearce_at_tenure.com

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