I have 3 drives. For this purpose, we will call them A, B and C respectively. 

A is 2 TB

B is 1 TB

C is 500 GB

I have already run 

```
rsync -avz -progress A B

```

Now B is full and I want to move/copy what is **not** already on B from A to C

It really doesnt matter to me what happens to what is on A as I will reformat anyways.