@woozle Thank you so much. In my case I was looking for the word "Remove" which wasn't actually there, and missed the eject Icon.

For anyone else with failing eyesight, the icon looks a bit like a badge with the up arrow eject symbol inside and is in the first "Storage Status" panel, below the "Modify" column.

Can't believe I didn't see that! 

It's like you go to the fridge and can't see the butter and it's there all along in front of you!

  @TenaciousDEK 

I do use this icon and the disk disappears from the list. I also noticed that it's still connected and powered up by router, with a diode on and a disk inside spinning.

If I then proceed and I disconnect the drive, it seems to power down unsafely with an unpleasant sound. Am I doing something wrong or it's supposed to work this way?