In this paper, we study energy conservation techniques for disk array-based network servers. First, we introduce a new conservation technique, called Popular Data Concentration (PDC), that migrates frequently accessed data to a subset of the disks. The goal is to skew the load towards a few of the disks, so that others can be transitioned to low-power modes. Next, we introduce a user-level file server that takes advantage of PDC. In the context of this server, we compare PDC to the Massive Array of Idle Disks (MAID). Using a validated simulator, we evaluate these techniques for conventional and two-speed disks and a wide range of parameters. Our results for conventional disks show that PDC and MAID can only conserve energy when the load on the server is extremely low. When two-speed disks are used, both PDC and MAID can conserve significant energy with only a small fraction of delayed requests. Overall, we find that PDC achieves more consistent and robust energy savings than MAID.

In this paper we study four approaches to conserving disk energy in high-performance network servers. The first approach is to leverage the extensive work on laptop disks and power disks down during periods of idleness. The second approach is to replace high-performance disks with a set of lower power disks that can achieve the same performance and reliability. The third approach is to combine high-performance and laptop disks, such that only one of these two sets of disks is powered on at a time. This approach requires the mirroring (and coherence) of all disk data on the two sets of disks. Finally, the fourth approach is to use multi-speed disks, such that each disk is slowed down for lower energy consumption during periods of light load. We demonstrate that the fourth approach is the only one that can actually provide energy savings for network servers. In fact, our results for Web and proxy servers show that the fourth approach can provide energy savings of up to 23%, in comparison to conventional servers, without any degradation in server performance.

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In this paper we study four approaches to conserving disk energy in high-performance network servers. The first approach is to leverage the extensive work on laptop disks and power disks down during periods of idleness. The second approach is to replace high-performance disks with a set of lower power disks that can achieve the same performance and reliability. The third approach is to combine high-performance and laptop disks, such that only one of these two sets of disks is powered on at a time. This approach requires the mirroring (and coherence) of all disk data on the two sets of disks. Finally, the fourth approach is to use multi-speed disks, such that each disk is slowed down for lower energy consumption during periods of light load. We demonstrate that the fourth approach is the only one that can actually provide energy savings for network servers. In fact, our results for Web and proxy servers show that the fourth approach can provide energy savings of up to 23%, in comparison to conventional servers, without any degradation in server performance.

General questions Question f) How well does UK IP system promote innovation? Patents In areas where it is appropriate and managed properly, if the benefits outweigh the costs and are superior to alternative mechanisms, the patent system can play a positive role in stimulating innovation, and enhancing economic growth and improved quality of life for the benefit of all in society. The challenge is to design a patent system that does not present excessive costs on society, through for example unreasonable restrictions on access to new inventions, or harm to other non-patent systems that would otherwise stimulate inventive activity. The patent system is only used in certain areas of the economy. Some types of inventive activity are not subject to patents, and some types of research and development do not benefit from patent protection. The limited role for the patent system is deliberate, and recognizes the importance of other mechanisms, incentives, rewards, tendencies, and forces in the process of innovation and progress in the arts and sciences.