On Feb 5, 2012, at 10:32 AM, Phil Schaffner <Philip.R.Schaffner@xxxxxxxx> wrote:
> Boris Epstein wrote on 02/04/2012 11:57 AM:
>> What is RAID0+1?
>
> Nested RAID. Paraphrasing http://en.wikipedia.org/wiki/RAID :
>
> For a RAID 0+1, drives are first combined into multiple level 0 RAIDs
> that are themselves treated as single drives to be combined into a
> single RAID 1.
Probably the worse setup, a failure on both sides of a mirror means total loss and with the # of disks on each side of this setup the chance of this is much greater, recovery from a failure is a lot longer cause the whole stripe needs to re-mirror. While performance of reads is equal to 1+0 the writes are equal to a single mirror cause both sides need to complete before the next operation can run or only one write operation on the array at a time.
Much better RAID level is 1+0 which is a series of mirrors striped together. While a failure on both sides of any one mirror is total for the array there is only 1 disk on either side so the odds are less, recovery from failure is faster as well cause only one disk needs to be re-mirrored. Performance of reads and writes are equal because each mirror can perform writes independant of the others, or # of write operations equal to the number of mirrors.
-Ross
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