You may want to see the following post even though its for the first gen v4.x single bay My Cloud units. It may give you some pointers:
https://community.wd.com/t/clean-os-debian-openmediavault-and-other-firmwares/93714/870
Or see this link from Fox_exe: https://drive.google.com/file/d/0B_6OlQ_H0PxVclJPMWpKcFdkZEk/view
Again, those directions are for the first gen My Cloud and may not be valid or work for the second gen My cloud but it may give you some direction on where to start looking in getting OVM to spin down.
