MyBook 3TB - prep for reinserting drive after 'borrowing' it

Hi
Recently I had to pop the drive out of my MyBook 3TB drive and use it for an urgent issue.
I now wish to reinsert it back into its enclosure.

However, when I have inserted it into the drive it only shows 1.8TB instead of 3TB! I didnt take not of any special partitions or partition types (MBR/GPT etc) before formatting as i assumed the onboard firmware would just reformat once it was reinserted.

I have tried wiping it, zeroing it out and other methods but still only get 1.8TB. Its like its hitting the 2TB limit but if its a wiped drive there should me no MBR setting etc. Or have i missed something basic?

Does anybody know how a drive should be prepared before reinsertion into the enclosure?

Thanks