Disk management for a hard real-time file system
Proceedings of the Eighth Euromicro Workshop on Real-Time Systems
© Raymond Man Kit Cheng, 1995 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be^ granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall
... ncial gain shall not be allowed without my written permission. The University of British Columbia Vancouver, Canada Department DE-6 (2/88) 11 Abstract The problem of scheduling disk requests in a personal hard real-time read/write file system is examined. It is shown that any optimal algorithm for a simplified disk scheduling can be forced to thrash very badly. To avoid thrashing, we propose a fixed-period scan (FSC AN), approach for disk scheduling in our file system. The idea is to use the CSCAN policy to pick up the data blocks requested by a periodic preemptive schedule. The approach trades disk block size and memory buffer size for higher performance. We derive the worstcase seek and rotational overhead for the FSCAN algorithm, and we show that the worst-case seek overhead can be measured empirically for a large class of seek functions. Using this approach and utilizing measured seek functions from real disk drives, we show that^these policies can transfer data at 40-70% of the maximum transfer rate of modern disk drives, depending on the file system parameters. A configuration program is developed to automatically test and configure the FSCAN algorithm for modern hard disks. The design, implementation and testing of this program are described. Abstract ii List of Figures v List of Tables vii Acknowledgement viii 71 Appendix: Sample Runs of the Configuration Software 75 A.1 The DISKSCAN program 75 A. 1.1 Data file for the Micropolis 4110 drive , 77 A. 1.2 Data file for the Quantum LPS540S drive 78 A.2 The FSCAN program . 80 A.2.1 Sample run of the FSCAN program 81 A.2.2 MATLAB® M-file output 82 Vlll Acknowledgement I would like to express my sincere thanks to my thesis supervisor, Dr. Donald Gillies, for introducing me to this thesis topic and for his continuous guidance in the past year. His remarkable knowledge in real-time system and his insight on this topic have been a great help to me. His patience, perceptiveness and encouragement are deeply appreciated. I would also like thanks my program supervisor, Dr. Mabo Ito, who grants me generous help and freedom in my research. Special thanks to Dr. Mark Greenstreet for his constructive criticisms and precious opinions toward my work. Acknowledgements to Kendra Cooper for her valuable comments on an earlier draft of this work. Many thanks also to Jeffrey Chow, John Jay Tanlimco, Darren Tsang, Steve So, Gary Yam and other colleagues who make my experiences as a graduate student filled with joyful memories. Warmest thanks to my respectable father, my prudent mother, my keen brother Terry, and my lovely sisters Selina and Pinky. Their immeasurable love and support will never be forgotten. My special gratitude go to Winnie Ho, who gives me continuous moral support and immense care throughout my work. Warm thanks to everyone in EP-Cell, who encourage and support me in prayers. I thank God for giving me such a good family and wonderful friends. Thank Him for granting me the opportunity to study and the needed wisdom to finish this work. It is only through Him that all thing are made possible.