Improving Reliability of Energy-Efficient Storage Systems

Abstract

With the rapid growth of the production and storage of large scale data sets it is important to investigate methods to drive the cost of storage systems down. Many energy conservation techniques have been proposed to achieve high energy efficiency in disk systems. Unfortunately, growing evidence shows that energy-saving schemes in disk drives usually have negative impacts on storage systems. Existing reliability models are inadequate to estimate reliability of parallel disk systems equipped with energy conservation techniques. To solve this problem, we firstly propose a mathematical model - called MINT - to evaluate the reliability of a parallel disk system where energy-saving mechanisms are implemented. In this dissertation, MINT is focused on modeling the reliability impacts of two well-known energy-saving techniques - the Popular Disk Concentration technique (PDC) and the Massive Array of Idle Disks (MAID). Different from MAID and PDC which store a complete file on the same disk, the Redundancy Array of Inexpensive Disks (RAID) stripes file into several parts and stores them on different disks to ensure higher parallelism, hence higher I/O performance. However, RAID faces more challenges on energy efficiency and reliability issues. In order to evaluate the reliability of power-aware RAID, we then develop a Weibull-based model–MREED. In this dissertation, we use MREED to model the reliability impacts of a famous energy efficiency storage mechanism– the Power-Aware RAID (PARAID). Thirdly, we focus on validation of two models–MINT and MREED. It is challenging to validate the accuracy of reliability models, since we are unable to watch certain energy-efficiency systems for a couple of decades due to its time consuming and experimental costs. We introduce validated storage system simulator–DiskSim–to determine if our model and DiskSim agree with one another. In our validation process, we compare a file access trace in a real-world file system. Last part of of this dissertation focuses on improvement of energy-efficient parallel storage systems. We propose a strategy–Disk Swapping–to improve disk reliability by alternating disks storing data that is frequently accessed with disks holding less accessed data. In this part, we focus on studying reliability improvement of PDC and MAID. At last, we further improve disk reliability by introducing multiple disk swapping strategy.