[CentOS] distributed storage/home-made cloud recommendations

Sun Feb 5 22:31:40 UTC 2012
Ross Walker <rswwalker at gmail.com>

On Feb 5, 2012, at 10:32 AM, Phil Schaffner <Philip.R.Schaffner at NASA.gov> 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.