Re: Storage EMC

Jared,

I always thought the opposite, that  RAID 1+0 is more fault-tolerant,
based on a paper I downloaded.  Excerpt:

In either case (0+1 or 1+0), the loss of a single drive does not
result in failure of the RAID system. The difference comes in the
chance that the loss of a second drive from the system will result in
the failure of the whole system. In RAID 0+1, you have to lose one
drive from each disk set to result in the failure of the whole system.
 In RAID 1+0, you have to lose all drives in a mirror.

Mathematically, the difference is that the chance of system failure
with two drive failures in a RAID 0+1 system with two sets of drives
is n/(2n-2) where n is the total number of drives in the system. The
chance of system failure in a RAID 1+0 system with two drives per
mirror is 1/(n-1). So, using the 8 drive systems shown in the diagrams
[not included here, sorry], the chance that losing two drives would
bring down the RAID system is 4/7 with a RAID 0+1 system and 1/7 with
a RAID 1+0 system.

Paul Baumgartel

On 6/9/05, Jared Still <jkstill@xxxxxxxxx> wrote:
> RAID 0+1 is more fault tolerant than RAID 1+0.
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