Mybook essential LED slowly blinking

Mybook is connected to my synology NAS, it is set to hibernate external usb harddisk after 10 mins idle. I can see after 10+ min idle, mybook’s led starts to slowly blink, does it mean mybook goes into hibernation mode(hard disk not spin any more?)?

You can test that by connected the drive to your computer and check if it does go to sleep there.

How can I know if mybook is in the sleep/hibernation mode? by LED?

And you won’t be able to access it.

So what does LED slowly blinking mean? In this state, does hard disk still spin?