Systems, methods, and machine readable media for repairing data processing systems. A first head is actuated over the first disk surface and a second head is actuated over the second disk surface. The contactor units are formed, tested, and assembled to a backing substrate. The through-wafer via device further comprises a conductive layer made of the conductive material and formed on the side of the first wafer surface, the conductive material filling the first trenches such that the first conductive layer has a substantially planar and closed surface. The method may include: reading a first signal with a reader head of the reader at a pre-determined position of the storage medium; reading a second signal with a reader head of the reader at the pre-determined position of the storage medium; and determining data stored at the pre-determined position of the storage medium based on the first signal and based on the second signal.