While my PC is switched OFF, HDD are still active.

[carnageX]

Just because the power light is on, doesn't mean it's spinning / active. Most drives nowadays (including externals) go into a low power/sleep mode even when your computer is on after they've been idle for a period of time to save power/wear.

If you want to disable that, check your BIOS settings. Or just unplug them when not in use.

 

[PP Mguire]

Like was said before, just because they have an on light doesn't mean they are actively spinning. That being said, the drives in my server stay powered and spinning 24/7 and have been for years without issue. One of them going on 7 years now.

This PC you have now is a new PC and it is the norm to have USB ports that are active while the computer is off to charge things like phones, tablets, and wireless controllers/headsets. These are usually USB 3/3.1 ports. It's why I asked previously which ports these drives are plugged into because typically USB2 ports are still shut off while the PC is off. If you're really that worried about it then just either unplug your drives or use a USB hub and extension to unplug while not in use. (Extension so there's no wear on the HDD plugs or ports on PC motherboard)