I'm trying to get a couple of drives in my system to sleep and stay asleep. They have other OS's on them, and I have no need to ever access them from linux. They are not mounted. I run hdparm -Y on them, and they go to standby. about 10 min later I can check them (hdparm -C) and they are active/idle again.
What would cause an unmounted drive to spin up after being put to sleep?