Yeah I created a VM to "refresh" my backup in the mean time.

I hadn't realised the data de-duplication wasn't working across devices. That's not great then.

I actually pointed my VM at my complete restore so it should have been a 100% identical copy of the current state (albeit in a slightly different location. The data deduplication seems quite slow in some places. It got to about half way and then slowed as if it was backing up the files again which the logs seem to reflect too.