Can you describe exaclty what you want to acheive? If you install xsan on a macbook pro, it will never function as an MDC as a macbook pro has no fibre connection. You can upgrade a client to a controller, switch the macbook pro off, connect your xserve and enter the licence from the macbook pro, and set your xserve to be a controller. Then change your current controller back to a client. It is quite a dangerous thing running with only one mdc though. If you loose that, you loose your data!