How to transfer backups from a current backup drive to a new backup drive

On advice from an apple Time Machine forum I copied backup data from the original WD drive to the new WD drive. That was 36 hours ago.
I’m only copying less than 1TB, what the heck is going on here? Is this normal?

How are you transferring the data into the new WD Drive?

The only safe and best way I would suggest you to transfer the data manually and into small pieces.

Then just transfer/copy one folder or file at a time