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Chapter 7 Drive Independent Recovery of Hard Disk Data ABSTRACT Title of dissertation: The Study and Development of Automatic Data Acquisition System for Spin-Stand Imaging and Drive Independent Recovery of Hard Disk Data Chun-Yang Tseng, Ph.D., 2007 Dissertation directed by: Professor Isaak D. Mayergoyz Department of Electrical and Computer Engineering In this thesis, an automatic data acquisition system for spin-stand imaging and drive independent data recovery is developed. This system enables a user to perform data acquisition of on-track hard disk data by using a commercial spin-stand. At the heart of this system are the three techniques: the track-centering technique, the dynamic track- following technique and the servo-based track-following technique. By using the track-centering technique, we are able to efficiently make the center of the prewritten data tracks coincide with the rotational center of the spin-stand spindle so that the track eccentricity can be eliminated. Both the dynamic track-following and servo- based track-following techniques utilize a small piezoelectric actuator (PZT) as the micro-positioning device. The former is of an open-loop controlling scheme, and the desired tracking trajectory is extracted from the whole-track spin-stand images. The latter is of a closed-loop feedback control scheme, and the feedback signals are from the existing servo patterns on the disk. The former deals with PZT hysteresis by using a special algorithm based on the Preisach model while the approach taken by the latter is based on iterative compensation. By using the developed techniques, we are able to perform spin-stand microscopy on hard disks with longitudinal and perpendicular modes of recording taken from latest commercial hard disk drives (HDDs) with ultra-high areal densities (as high as 131.5 Gbits/in2). The automatic data acquisition system has been successfully applied to recover actual hard disk data from failed HDDs. The Study and Development of Automatic Data Acquisition System for Spin-Stand Imaging and Drive Independent Recovery of Hard Disk Data by Chun-Yang Tseng Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2007 Advisory Committee: Professor Isaak D. Mayergoyz, Chair/Advisor Professor P.S. Krishnaprasad Professor Romel D. Gomez Professor Thomas E. Murphy Professor Dianne P. O’Leary © Copyright by Chun-Yang Tseng 2007 DEDICATION To my parents and family, for their love and continuous support during the entire time of my graduate studies. ii ACKNOWLEDGMENTS First and foremost, I would like to give my thanks and respect to my advisor, Prof. Isaak Mayergoyz, for his prudent guidance, unceasing encouragement, and tremendous inspiration to me. Through these years of my thesis research with him, I have learned a lot not only from his distinguished scientific talent and knowledge but also from his highly respectable virtues. His firm resolution and fearlessness toward obstacles encountered in scientific research has left a strong impression in me. He is definitely a great pattern of an explorer of sciences. I feel very grateful and fortunate to be one of his students during my Ph. D studies. I would also like to thank Dr. Charles Krafft for his advice and assistance for solving issues occurred in the research and experiments. I would like to acknowledge Dr. Chun Tse for introducing me to the spin-stand microscopy technique. I am grateful to Dr. Michael Dreyer for showing me the method of controlling the displacement of a piezoelectric actuator. I am indebted to Les Lorenz and Peter Krusen for helping me with the modification of the head cartridge of the spin-stand. I am also thankful to Lisa Lucas for instructing me to desolder magnetic recording heads from a commercial hard disk drive and to solder these heads with a proper interface for them to be functional on a spin-stand. Special thank to my fellow graduate student, Patrick McAvoy, with whom I endeavored on many challenging research projects. I would like to especially thank my wife, I-Chun, for her continuous support and understanding. Finally, I would like to thank my parents for their support and encouragement during the entire time of my graduate studies. iii TABLE OF CONTENTS Dedication . ii Acknowledgments . iii Table of Contents . iv List of Figures . viii List of Tables . xi List of Publications . xii Chapter 1 – Introduction . 1 1.1 Technological evolution of hard disk drives . 1 1.2 The spin-stand based magnetic microscopy . 5 1.3 The need for drive independent data recovery . 8 1.4 The need for an automatic data acquisition system . 13 1.5 Main results . 16 1.6 Dissertation Outline . 17 Chapter 2 – Track-Centering Technique . 20 2.1 The issue of eccentricity . 20 2.2 The track-centering algorithm . 23 2.3 Experiment and results . 25 2.4 Summary . 29 iv Chapter 3 – Dynamic Track-Following Technique . 31 3.1 Algorithm for extracting the trajectory of the data tracks . 32 3.2 The dynamics of the piezo-based positioning system . 34 3.3 Measurement of the hysteresis loop . 36 3.4 Algorithm for controlling a piezoelectric transducer . 37 3.5 Setup of dynamic track-following system and phase-locking system . 39 3.6 Experiments and results . 41 3.7 Summary . 43 Chapter 4 – Servo Positioning System . 44 4.1 Position error signal (PES) . 45 4.1.1 The 4-burst servo scheme . 45 4.1.2 The 2-burst servo scheme . 48 4.2 PES generation algorithm . 51 4.2.1 PES generation algorithm for the 4-burst servo scheme . 52 4.2.2 PES generation algorithm for the 2-burst servo scheme . 53 4.3 Setup of the servo positioning system . 55 4.4 Mechanism of the servo positioning system . 56 4.5 Experiments and results . 57 4.6 Summary . 58 Chapter 5 – Track-Following Technique Based on Servo Feedback . 59 5.1 Algorithm for real-time track following . 61 v 5.1.1 Algorithm for acquiring the trajectory of the data track by using the existing servo patterns . 62 5.1.2 Iterative compensation for the PZT hysteresis . 64 5.1.3 Proof for the convergence of the iterative algorithm . 66 5.2 Experiments and results . 69 5.3 Summary . 70 Chapter 6 – Spin-Stand Microscopy of Hard Disk Data . 72 6.1 Magnetic recording technology in hard disk drives . 73 6.1.1 Longitudinal recording . 74 6.1.2 Perpendicular recording . 75 6.2 Experiments . 76 6.3 Hard disk images . 78 6.4 Summary . 83 Chapter 7 – Drive Independent Recovery of Hard Disk Data . 84 7.1 Hard disk technology . 86 7.1.1 Hard disk geometry . 86 7.1.2 File system analysis . 91 7.1.3 Hard disk data encoding . 92 7.2 Procedures of spin-stand-based drive independent data recovery . 93 7.3 Experiments and results . 95 7.4 Summary . 100 vi Chapter 8 – Conclusions and Further Study . 101 8.1 Dissertation summary . 102 8.2 Future directions . 104 Appendix A . 106 Appendix B . 110 B.1 FAT file system . 110 B.2 Hard disk data encoding schemes . 112 B.2.1 Error correction encoding . 112 B.2.2 Channel encoding . 113 B.2.3 Data scrambler . 115 Bibliography . 117 vii LIST OF FIGURES 1.1 Areal density increase versus product year . 2 1.2 Average price of storage (from Hitachi Global Storage Technologies) . ..
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