DREAM-S (Distributed REAl time Main memory database management System) is a database management system for the ATM switching system. DREAM-S has distributed system architecture to support handling of distributed data in the ATM switching system. Although, conventional main memory database management systems can guarantee a high performance, reliability of the main memory database is a critical problem since the main memory is volatile. Backup system of DREAM-S should support not only the prevention of the data loss but also the consistency of database state. In addition, the backup system has to meet the ATM switching system's requirements: real-time processing, distributed architecture, and fault-tolerance. In this paper, we propose data backup system to reduce the penalties involved in maintaining consistency and to improve data availability in switching system. Especially, we describe a concurrent log processing scheme to meet the high performance and reliability of the real-time backup system on the database update requests. And we also introduce the results of analysis to prove that the proposed technique is effective techniques.