I have recently upgraded from Win 8.1 Pro x64 to Win 10 Pro x64 and I am experiencing a weird problem.
My HDD setup is as follows:
Samsung EVO 250GB M2 SSD - OS and apps
Crucial MX100 512GB SATA SSD - Games
Seagate ST2000 2TB SATA HDD - Media

After configuring Windows 10 to sleep the HDD (the seagate) after 5 mins of inactivity I noticed that it never actually does it, the HDD never goes to sleep.
That HDD only has media on it and no apps so there should be nothing accessing it.

How can I found out what is preventing the HDD from going to sleep?