Re: RAID 10 far and offset on-disk layouts

[Gionatan Danti <g.danti@assyoma.it>]

> <snip>
> Therefore the *probability* of loss of data because of 2 member
> devices failing is higher in layout 1) than layout 2), whether
> or not the drives are "adjacent".
>
>    Note that arguably layout 1) is not really RAID10, because an
>    important property of RAID10 is or should be that there are
>    only N/2 pairs out of N drives. Otherwise it is not quite
>    'RAID1' if a chunk position in a stripe can be replicated on 2
>    other devices, half the replicas on one and half on another.
>
> That the member devices are *adjacent* is irrelevant; what
> matters is the statistical chance, which is driven by the
> percent of cases where 2 failures result in data loss, which
> driven by the number of paired drives.

Very detailed answer, thank you Peter :)

Based on what keld told before, the current scheme if n.2 (wikipedia's 
one), right? It is possible, using mdadm, understand the physical layout 
(if n.1 or n.2) of a live RAID10 array?

As schema n.1 lead to increased probability of data loss, why offset 
layout use it instead of, say, some variance of schema n.2?

Regards.

-- 
Danti Gionatan
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