# create a raid1 array with a wrmostly device

mdadm -CR $md0 -l1 -n3 $dev0 $dev1 --write-mostly $dev2
testdev $md0 1 $mdsize0 64

# unfortunately, we cannot measure if any read requests are going to $dev2

mdadm -S $md0

mdadm -CR $md0 -l1 -n3 --write-behind --bitmap=internal $dev0 $dev1 --write-mostly $dev2
testdev $md0 1 $mdsize0 64
mdadm -S $md0