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© The Author 2010. Published by Oxford University Press on behalf of The British Computer Society. All rights reserved. For Permissions, please email: [email protected] Advance Access publication on June 18, 2010 doi:10.1093/comjnl/bxq053 Analytical and Simulation Modelling of Zoned RAID Systems Abigail S. Lebrecht, Nicholas J. Dingle and William J. Knottenbelt Department of Computing, Imperial College London, South Kensington Campus, SW7 2AZ UK Corresponding author: [email protected] RAID systems are ubiquitously deployed in storage environments, both as standalone storage solutions and as fundamental components of virtualized storage platforms. Accurate models of their performance are crucial to delivering storage infrastructures that meet given quality of service requirements. To this end, this paper presents a flexible fork-join queueing simulation model of RAID systems that are composed of zoned disk drives and which operate under RAID levels 01 or 5. The simulator takes as input I/O workloads that are heterogeneous in terms of request size and that exhibit burstiness, and its primary output metric is I/O request response time distribution. We also study the effects of heavy workload, taking into account the request-reordering optimizations employed by modern disk drives. All simulation results are validated against device measurements and compared with existing analytical queueing network models for the development of the models. Keywords: simulation; analytical models; queueing systems; RAID Received 26 May 2010; revised 26 May 2010 Handling editor: Erol Gelenbe 1. INTRODUCTION RAID 1 has revolutionized data storage because of its ability to synthesize a set of low-cost commodity storage devices into a single logical unit that can deliver high reliability with high performance. However, RAID system performance varies heavily in practice, depending on chosen configuration and operating context. Given a budget and an expected workload, it is therefore a major challenge for system designers and engineers to select RAID components and corresponding configurations capable of delivering a required level of quality of service. Performance models provide a low-cost means to evaluate the suitability of candidate system designs ahead of implementation. Within this context there has been a broad body of research work carried out over the last two decades directed at devising a variety of configuration [ 2 7 ], scheduling [ 8 11 ] and caching [ 12 21 ] strategies for improving RAID system performance. Most of these works make use of simulation as a means of evaluating the impact of proposed strategies. The present paper introduces a queueing-based simulator for the analysis of RAID systems comprising of zoned disks. Our goal is to provide an 1 Redundant Array of Independent Disks [ 1 ]; RAID levels describe various ways of spreading data across multiple storage devices using striping, mirroring and/or parity.
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  • Spring '12
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