Fail-safe WORM file system

Abstract

Most operating systems rely on recovery programs to repair the file systems after failures have occurred. The loss of data in high capacity storage devices is extremely costly. We illustrate how robust file systems may be built for the WORM optical disks. We define a model for the storing and updating of files in a file system. We identify the data structures in the file systems and their usage. We then suggest how to optimally store and organize these data structures. We also examine the different types of failures and their effects on the file systems. Next, we discuss how recovery programs may be designed for the WORM media. While files may be recovered after failures have occurred, we propose an alternate scheme in which invalid data are detected early. The scheme gives better protection and the loss of files is minimized. Finally, we present an approach for keeping duplicate copies of critical file management information.