hi peeps,

i've been reading through

http://en.wikipedia.org/wiki/Non-standard_RAID_levels

and just wanted to verify if my understanding is correct.

Is "near" safer than "far"?

e.g. given 4 drives in RAID10 array, n2:

4 drives

1 2 3 4
--------------
A1 A1 A2 A2
A3 A3 A4 A4
A5 A5 A6 A6
A7 A7 A8 A8

you'd lose the array if either 1&2 or 3&4 goes down at the same time.


With 4 drives in RAID10 array, f2:

4 drives
1 2 3 4
--------------------
A1 A2 A3 A4
A5 A6 A7 A8
A9 A10 A11 A12
.. .. .. ..
A4 A1 A2 A3
A8 A5 A6 A7
A12 A9 A10 A11

...there seems to be a lot more combinations that can result in a trashed array(1&2, 2&3, 3&4).

Is my analysis correct? Inputs are more than welcome, tia

Good question...wonder why no responses. I'm trying to figure out which drives to fail so I can shrink a 4-disk RAID10 to 2 separate RAID0 arrays, but I digress.

The 2nd part of your layout (at the bottom of post) is not correct:

1__2__3__4_
A1 A2 A3 A4
A5 A6 A7 A8
A9 A10 A11 A12
.. .. .. ..
A4 A1 A2 A3 <------
A8 A5 A6 A7 <------
A12 A9 A10 A11 <----

It should look like this:
1 2 3 4
_________________
A1 A2 A3 A4
A5 A6 A7 A8
A9 A10 A11 A12
.. .. .. ..
A2 A1 A4 A3 <----
A6 A5 A8 A7 <----
A10 A9 A12 A11 <---
.. .. .. ..

Devices 1&2 and 3&4 are still mirrors, the data is just stored on different parts of the media. I'm not sure about the safeness. It probably depends on how the drives fail. Maybe someone else can elaborate...