Just a short answer.
I didn't use the replace command.
I added the new drive to the pool / array, and checked that it was
registered.
Following that I removed the 1TB drive with "btrfs device delete <drive>".
As far as I know this should avoid the need to resize the new drive.
"btrfs fi us" shows all the space as available. The drive shows 1.7TB as
unallocated.
I have started moving some data of the array to give btrfs some more
room to move, and will follow what happens when I try a new balance
later on.
