Abstract. A power-saving management for OLTP applications has become an important task for user budgets and datacenter operations. This paper presents a novel power-saving method for multiple disk drives based on knowledge of OLTP application behaviors. We report detail analysis of power consumption of disk drives and I/O characteristics of OLTP application. We then show experimental and simulation results of our power-saving methods. Our method provides substantially lower power consumption of disk drives compared to that of a conventional OLTP environment. Key words: Database, Online Transaction Processing (OLTP), Disk Drive, Power-Saving