@Vinny - First, when you want help, you are more likely to get it if you provide all relevant info for your questions. For example, what OS are you using; would appear to be Windows but which version? What format is your HD, FAT, EXT2/3, NTFS? How are you mounting the drive on the router, automount? What properties are you checking to find how full it is?
Given your lack of providing such info, it is much harder to help you. As for how full your HD is, I can't say how to fix the method you are trying but you can telnet/ssh to the router and use the command:
The Mounted on
column identifies the partition for each row and the Available
column tells you how much is free.
As for the UNKNOWN name, it is probably that you did not label your partition. Provide the info found from the router GUI under USB and NAS>USB Support in the Attached Devices section the Description column for your disk - it can be copied and pasted. Then I or someone else can help you set the label if that is the problem.
As for disk spin down, see sd-idle-2.6 (I am the author). If your disk is actively used 24/7 then spin down does not make sense. But if it is idle for long periods (eg over night) then it makes sense as it saves energy and disk wear.