Just a service note for those still working with an R4 pro. KingSpec PATA IDE 44 Pin 2.5" SSD drives are fully compatible both physically and electronically. They offer various capacities. I installed the 128 GB and R4 pro booted without difficulty.
Those contemplating working with the r4 PRO and the Remote Audio's BDS need to be aware that the r4 PRO does not have positive/negative ground protection on the 4 pin external power socket. This means that if you attach the wrong device, i.e. a radio mic with the wrong ground polarity, you will fry the power input on the r4 pro. Roland does not do ANY component level repairs for this unit. So this mistake will cost $250 for a new main board.