Stochastic Evaluation of Magnetic Head Wears in Hard Disk Drives

Head wear becomes inevitable as the physical clearance between the head and disk in current hard disk drives is close to 1 nm or lower. Accurate characterization of the wear process is essential in understanding the wear mechanism, evaluating the reliability of hard disk drives (HDDs), and predicting the future evolution of wear as well as guiding the design of HDDs of later vintages. Due to the variations in the material and geometry of magnetic head, the wear process is dynamic and stochastic. To cope with the dynamics, a Wiener process with a positive drift is used to model the wear process. Furthermore, to evaluate the reliability quickly, an accelerated degradation model using the wear measurements is developed, from which the parameters/failure times under light loads can be effectively predicted. The developed model is then applied to a real wear problem of magnetic head to demonstrate the effectiveness.