This topic doesn't seem to be a clean fit for any of the listed forums, but this one seems to be most close to being relevant. 

I have a DS214+ (2-disk bays) Synology NAS with 2 x 3TB raid-mirrored hard drives.

I also have two external USB drives plugged into it and one of them ("usbshare1")  is a share known as "usbshare".

The NAS reports as being 94% full (of the 2.5TB available).

But digging in to the detail, fully 1.2TB of this is "usbshare".....which is actually the external hard drive.

Why are the files on the external drive counting as being on my internal 2.5TB of space?

I can't work it out so far.....Maybe I indexed it and that resulted in it essentially being copied over?

Anyone have any suggestions? Looks like I've missed something big....and I would like my 1.2TB back.

I'm on the latest version of the OS: DSM 6.1-15047 Update 2