Yuzuru Maya

Two-Phase Majority Decision Scheme Using Time-Stamps

Mission critical files are shared through networks, making file manipulation a serious problem. In a system consisting of a main-node and sub-nodes, I propose a two-phase majority decision scheme using time-stamps as an identifier in order to solve this problems. In the first phase, the main-node checks the time stamps of its own files and files them in sub-nodes. If the results are effective, the main-node sets the files as members of the majority decision scheme. In the second phase, the main-node runs the majority decision scheme from the selected files. I evaluated the reliability and MTBF of the conventional and proposed majority decision scheme. I also show that the reliability and MTBF of the proposed scheme is 2-4 times of that of conventional scheme and that the proposed scheme is suitable for multi-faults of files.

A high-speed recovery method for use in distributed computer systems

A system is proposed for high-speed switching from the on-line unit to the back-up unit in hot-standby systems for high reliability. In a hot-standby system it is necessary to transfer periodically the memory contents of the on-line unit as checkpoint data to the memory of the back-up unit so that the back-up unit can take over in case of a system fault. The proposed method guarantees that there is no file update between consecutive checkpoints by transferring checkpoint data whenever a file is updated. Because of that, the journal for file recovery is not necessary, thus making the downtime short. The downtime and overhead of this method are compared quantitatively with those of the conventional method. The results show that in this proposed method the overhead is within the allowable range, the downtime is about 2 s, and the system downtime cannot be recognized by users.