a synchronization technique is described which finds use in a disk array subsystem comprising a plurality of disk storage devices connected to a controller . in response to signals from each of the devices specifying their angular position at a particular time , the controller calculates the relative angular positions of the devices and issues a signal to each of the devices specifying the amount and direction of change in rotational velocity required to achieve synchronization . in a two device subsystem , the signal to one device will specify a speed decrease and the signal to the second device will specify a speed increase .