Using system structure and semantics for validating and optimizing performance of multi-tier storage systems

Modern persistent storage systems must balance two competing imperatives: they must meet strict application-level performance goals and they must reduce the operating costs. The current techniques of either manual tuning by administrators or by over-provisioning resources are either time-consuming or expensive. Therefore, to reduce the costs of management, automated performance-tuning solutions are needed.\n\nTo address this need, we develop and evaluate algorithms centered around the key thesis that a holistic semantic-aware view of the application and system is needed for automatically tuning and validating the performance of multi-tier storage systems. We obtain this global system view by leveraging structural and semantic information available at each tier and by making this information available to all tiers. Specifically, we develop two key build- ing blocks: (i) context-awareness, where information about the application structure and semantics is exchanged between the tiers, and (ii) dynamic performance models that use the structure of the system to build lightweight resource-to-performance mappings quickly. We implement a prototype storage system, called Akash, based on commodity components. This prototype enables us to study all above scenarios in a realistic rendering of a modern multi-tier storage system. We also develop a runtime tool, Dena, to analyze the performance and behaviour of multi-tier server systems.\n\nWe apply these tools and techniques in three real-world scenarios. First, we leverage application context-awareness at the storage server in order to improve the performance of I/O prefetching. Tracking application access patterns per context enables us to improve\nthe prediction accuracy for future access patterns, over existing algorithms, where the high interleaving of I/O accesses from different contexts make access patterns hard to recognize. Second, we build and leverage dynamic performance models for resource allocation, providing consistent and predictable performance, corresponding to pre-determined application goals. We show that our dynamic resource allocation algorithms minimize the interference effects between e-commerce applications sharing a common infrastructure. Third, we introduce a high-level paradigm for interactively validating system performance by the system administrator. The administrator leverages existing performance models and other semantic knowledge about the system in order to discover bottlenecks and other opportunities for performance improvements. Our evaluation shows that our techniques enable significant improvements in performance over current approaches.

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