dm-raid usage setup

[Benoit Gschwind]

Hello,

Is it fine and sane to stack raid device using dm-raid, i.e. raid-0
above raid-6 ?

Is it fine and sane to use raid-0 for the raid-6 journal ?

Is it fine and sane to use same disks into several different raid, i.e.
splitting disk into two or more partitions and using this partitions as
disk for different raid ?

Thanks by advance