A system for predicting the failure of a storage unit, such as a disk drive. In a most general sense, the inventive system includes a first mechanism (20, 22, 24) for moving an element (16) over a surface (12) which is moving relative to the element (16). The first mechanism includes an arm (18, 20) for supporting the element (16) over the surface (12) and a motor (24) connected to the arm (18, 20). A position error detector (42) is included for detecting a change in torque applied to the motor (24) due to friction between the element (16) and the surface (12). The position error detector (42) provides a signal in response to changes in torque which is processed to predict a head disk interaction or failure of the storage system. In a particular embodiment, the position error detector (42) senses a change in a lateral force applied to the element (12) in response to a change in friction between the surface and the element. In a typical application, the storage unit is a disk drive, the surface is a disk on which a storage medium is disposed and the element is a magnetic head. In an alternative embodiment, changes in friction between the head and the medium are sensed by sensing changes in the motor current required to maintain disk speed.
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