Load balance across members of a N-way mirror set, and
handle the meta-RAID levels: R10, R50, R60.
Signed-off-by: NScott Teel <scott.teel@hp.com>
Signed-off-by: NStephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>