Copied External Drive with Disk Utility - Now they're linked?

I purchased an WD Easystore 8TB external drive and copied 3TB of data over from my existing WD MyBook using Disk Utility (Mac - process outlined at link below).

Now the two drives seemed to be linked? I can’t mount the 8TB drive without having the USB for the 3TB plugged into the Mac and when the 8TB drive is plugged in by itself, nothing shows up.

When I open disk utility it says that the 3TB drive (MyBook) has 5TB of disk space free and the 8TB drive (Easystore) is full…? See images at links below. How can this be?

Basically, I can’t view the data on the Easystore without the MyBook plugged in - but I can view the MyBook without the Easystore plugged in, but now it tells me that there’s 5TB free when it’s only a 3TB drive?

How can I fix this?
Thanks,
Steve

3TB Drive:
https://postimg.org/image/69rjdpcwd/

8TB Drive
https://postimg.org/image/y9vmxxycd/