The growth of business enterprises and the emergence of the Internet as a medium for data processing has led to a proliferation of applications that are server-centric. The power dissipation of such servers has a major consequence not only on the costs and environmental concerns of power generation and delivery, but also on their reliability and on the design of cooling and packaging mechanisms for these systems. This paper examines the energy and performance ramifications in the design of disk arrays which consume a major portion of the power in transaction processing environments. Using traces of TPC-C and TPC-H running on commercial servers, we conduct in-depth simulations of energy and performance behavior of disk arrays with different RAID configurations. Our results demonstrate that conventional disk power optimizations that have been previously proposed and evaluated for single disk systems' (laptops/workstations) are not very effective in server environments, even if we can design disks than have extremely fast spinup/spindown latencies and predict the idle periods accurately. On the other hand, tuning RAID parameters (RAID type, number of disks, stripe size etc.) has more impact on the power and performance behavior of these systems, sometimes having opposite effects on these two criteria.