Re: RAID 10 far and offset on-disk layouts

<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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