The author describes the implementation of a stable storage system which converts several fallible disk stores into reliable devices for storing data. It provides reliable reading and writing of data in a distributed UNIX environment, in spite of transient I/O faults, decay of physical storage devices, and processor crashes. The implementation makes available to UNIX users the facilities of a stable storage system: it provides the abstaction of stable files and maintains the standard UNIX system call interface; it also provides the system administration functions of verification and crash recovery. The implementation systematically handles abnormal situations by separating normal and exceptional processing in both the system description and implementation. This is achieved through the use of a fault tolerance design notation and the implementation of that notation using an exception handling package. Implementation code fragments and performance comparison measurements are included in the paper.

The author presents a clear, well-developed description of the motivation, design methodology, and implementation of the stable storage facility. There is considerable attention to the exposition of the design, design notation, interface, and implementation. The author states that the method of determining valid data write operations is best suited to append-only files.