Removing a "Free" disk

I wish to remove a bunch of drives from a TS843-UPX NAS (QTS 5.2.3-3006 - latest as of today).

The only mention I’ve found, in a range of forums/google, is under “Storage & Snapshots/Disks”, select the disk, click on “Remove” or “Disconnect”. Neither option exists on this box.

I am assuming its not safe to just Pull the drive as it’s still powered on at this point.

Under Linux I could udisksctl power-off -b /dev/sdx but I am assuming QTS has an equivalent hidden somewhere within the GUI.

Anyone any suggestions ?