Multi-speed Disks Research Articles

Minimizing Power Consumption in Video Servers by the Combined Use of Solid-State Disks and Multi-Speed Disks

Disks use a considerable portion of the total energy consumed by a video server. Solid-state disks (SSDs) can be used as a cache to reduce disk speeds, thereby decreasing the power consumed by disks. However, effective SSD bandwidth management is essential to cope with the high request rates for popular video files stored on SSDs. To address this problem, we propose a new SSD cache management scheme for a video server that uses multi-speed disks. First, we introduce a storage allocation scheme to examine how the presence of an SSD cache affects disk bandwidth consumption. We then propose an SSD bandwidth allocation algorithm to minimize energy consumption by allowing disks to run at lower speeds while achieving jitter-free disk speed transitions and by limiting the number of transitions to ensure disk reliability. Our experimental results demonstrate that our proposed bandwidth allocation algorithm achieves appreciable power savings under various workloads while limiting the number of disk speed changes.

An Energy-Efficient and Reliable Storage Mechanism for Data-Intensive Academic Archive Systems

Previous studies proposed energy-efficient solutions, such as multispeed disks and disk spin-down methods, to conserve power in their respective storage systems. However, in most cases, the authors did not analyze the reliability of their solutions. According to research conducted by Google and the IDEMA standard, frequently setting the disk status to standby mode will increase the disk’s Annual Failure Rate and reduce its lifespan. To resolve the issue, we propose an evaluation function called E 3 SaRC (Economic Evaluation of Energy Saving with Reliability Constraint), which considers the cost of hardware failure when applying energy-saving schemes. We also present an adaptive write cache mechanism called CacheRAID. The mechanism tries to mitigate the random access problems that implicitly exist in RAID techniques and thereby reduce the energy consumption of RAID disks. CacheRAID also addresses the issue of system reliability by applying a control mechanism to the spin-down algorithm. Our experimental results show that the CacheRAID storage system can reduce the power consumption of the conventional software RAID 5 system by 65% to 80%. Moreover, according to the E 3 SaRC measurement, the overall saved cost of CacheRAID is the largest among the systems that we compared.

Saving Energy in Video Servers by the Use of Multispeed Disks

Energy consumption is an important issue in data centers, and disks use a significant proportion of the total energy. A promising approach to reducing disk energy consumption is to use multispeed disks with lower rotational speeds, and allowing disks to run slowly when workloads are light can reduce their large contribution to the power used by video servers. We formulate the prerequisites for speed reductions, and derive an energy model constrained by retrieval period. We then analyze the relationship between retrieval period, buffer size, and disk speed, and examine the effect of buffer allocation on energy consumption. We then propose a new video data retrieval scheme in which the retrieval period and the speed of each disk is dynamically changed to adjust disk bandwidth utilization, with the aim of allowing disks to run at lower speeds while guaranteeing jitter-free speed transitions. Experimental results show that our scheme achieves appreciable energy savings under all workloads. They also reveal that increasing the number of available speeds reduces energy consumption but the benefits gradually tail off.

ERAID: Conserving Energy in Conventional Disk-Based RAID System

Recently, high-energy consumption has become a serious concern for both storage servers and data centers. Recent research studies have utilized the short transition times of multispeed disks to decrease energy consumption. Manufacturing challenges and costs have so far prevented commercial deployment of multispeed disks. In this paper, we propose an energy saving policy, eRAID (energy-efficient RAID), for conventional disk-based mirrored and parity redundant disk array architectures. eRAID saves energy by spinning down partial or the entire mirror disk group with constraints of acceptable performance degradation. We first develop a multiconstraint energy-saving model for the RAID environment by considering both disk characteristics and workload features. Then, we develop a performance (response time and throughput) control scheme for eRAID based on the analytical model. Experimental results show that eRAID can save up to 32 percent energy while satisfying the predefined performance requirement.

Hibernator

Energy consumption has become an important issue in high-end data centers, and disk arrays are one of the largest energy consumers within them. Although several attempts have been made to improve disk array energy management, the existing solutions either provide little energy savings or significantly degrade performance for data center workloads.Our solution, Hibernator, is a disk array energy management system that provides improved energy savings while meeting performance goals. Hibernator combines a number of techniques to achieve this: the use of disks that can spin at different speeds, a coarse-grained approach for dynamically deciding which disks should spin at which speeds, efficient ways to migrate the right data to an appropriate-speed disk automatically, and automatic performance boosts if there is a risk that performance goals might not be met due to disk energy management.In this paper, we describe the Hibernator design, and present evaluations of it using both trace-driven simulations and a hybrid system comprised of a real database server (IBM DB2) and an emulated storage server with multi-speed disks. Our file-system and on-line transaction processing (OLTP) simulation results show that Hibernator can provide up to 65% energy savings while continuing to satisfy performance goals (6.5--26 times better than previous solutions). Our OLTP emulated system results show that Hibernator can save more energy (29%) than previous solutions, while still providing an OLTP transaction rate comparable to a RAID5 array with no energy management.