High-availability scheme for shared servers of cluster systems using commands transfer

For cluster systems consisting of multiple processing nodes and shared serv ers which consist of an on-line and a backup shared server, we propose a ho t-standby scheme for shared servers. In this scheme for shared servers, whe n the on-line shared server receives a command from a node, it sends only a n update command and its data identifier to the backup shared server. Both the on-line and the backup shared server execute the update command indepen dently, and the command result of the on-line shared server is identical to that of the backup shared server. When the on-line shared server fails. th e backup reconstructs the shared data by using its own shared data and the user data from each node. We evaluated the system recovery time and the per formance overhead for this hot-standby scheme. It enables the performance o verhead to be ignored, and the system recovery time to be shortened to 20 s econds in cluster systems.