I similar problem and this post solves it: http://serverfault.com/questions/688207/how-to-auto-start-degraded-software-raid1-under-debian-8-0-0-on-boot
I similar problem and this post solves it: http://serverfault.com/questions/688207/how-to-auto-start-degraded-software-raid1-under-debian-8-0-0-on-boot