[CentOS] mdadm Linux Raid 10: is it 0+1 or 1+0?

[Miguel Medalha]

> If someone knows the answer, please also tell us whether it is the same 
> quality as using the raid0 module to drive two raid1 module arrays. This 
> raid10 module is rather new.

Meanwhile, I found some answers. Here's a document from Novell which 
discusses the matter, considering the 10, 1+0 and 0+1 variants:

Comparison of RAID10 Option and Nested RAID 10 (1+0)
http://www.novell.com/documentation/sles10/index.html?page=/documentation/sles10/stor_evms/data/b57a7ve.html

(There's a pdf version here: 
http://www.novell.com/documentation/sles10/pdfdoc/stor_evms/stor_evms.pdf )

It says:

"In mdadm, the RAID10 level creates a single complex software RAID that 
combines features of both RAID 0 (striping) and RAID 1 (mirroring). Multiple 
copies of all data blocks are arranged on multiple drives following a 
striping discipline. Component devices should be the same size."

mdadm module RAID10 uses a Near Layout and a Far Layout on the component 
disks. The document illustrates those layouts

mdadm RAID10 will be simpler than RAID0 over RAID1 since it only involves 
one software layer instead of two.
Both systems have advantages and disadvantages according to typical use.