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.