Abstract: The communications statuses of a plurality of clients are checked in a fixed cycle; when a check result corresponding to at least one of the clients is irregular, the estimated number of clients which will be able to receive communications services from an alternative server (standby server) after the server is switched from a main server (present server) to the alternative server is calculated based on all said check results; the calculated number of clients is compared with the number of clients which are receiving the communications services from the main server prior to the switch, and the appropriateness of the switch is determined based on the result of this comparison; the switch from the main server to the alternative server is controlled based on the result of the determination.

Abstract: A data processing system having an efficient logging mechanism which stores log records for repairing a file system when its consistency is lost. When there is a transaction attempting to update metadata stored in metadata volumes, a metadata loading unit reads the requested metadata objects out of the volumes and loads them to a metadata cache. At that time, a metadata manager updates its internal database to record from which metadata volume each metadata object has been fetched. Each time the transaction updates a metadata object in the cache, a log collection unit collects a copy of the updated metadata object, together with a volume ID which indicates its home metadata volume. The collected data is temporarily stored in a log buffer, and finally saved into a log volume by a log writing unit.