A File-System-Aware FTL Design for Flash-Memory Storage Systems

隨著快閃記憶體被廣泛的應用在眾多平台上，因快閃記憶體的特性而造成系統效能下降的問題也變得更為重要。本篇研究提出了一個檔案系統感知的快閃記憶體轉換層次設計，其中篩選機制將會區分出存取元資料(metadata)的請求並藉以提升系統效能；同時也提出了修復機制以維持檔案系統的健全性。所提出的快閃記憶體管理機制實作在Linux裝置驅動程式中，並且評估在ext2和ext3兩種檔案系統上的效能，在針對NTFS檔案系統以一系列真實的傳輸記錄做實驗，實驗結果在ext2、ext3和NTFS檔案系統上展現顯著的效能提升，並僅造成有限的額外負擔。As flash memory became popular over various platforms, there is a strong demand on the performance degradation problem, due to the special characteristics of flash memory. This research proposes the design of a file-system-aware flash translation layer, in which a filter mechanism is designed to separate the access requests of file metadata and contents for better performance. A recovery scheme is also proposed to maintain the integrity of a file system. The proposed flash translation layer is implemented as a Linux device driver and evaluated with respect to ext2 and ext3 file systems. Experiments were also done over NTFS by a series of realistic traces. The experimental results show significant performance improvement over ext2, ext3, and NTFS file systems with limited system overheads.List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viist of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viihapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 1hapter 2 SYSTEM ARCHITECTURE AND RESEARCH MOTIVATION 5.1 System Architecture . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Research Motivation . . . . . . . . . . . . . . . . . . . . . . . 7hapter 3 A FILE-SYSTEM-AWARE FTL DESIGN . . . . . . . . . 10.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 MFTL: A Metadata Management Scheme . . . . . . . . . . . 12.3 Reliability versus Commit Actions . . . . . . . . . . . . . . . 17.3.1 Implementation Remarks . . . . . . . . . . . . . . . . 20hapter 4 PERFORMANCE EVALUATION . . . . . . . . . . . . . 22.1 Performance Metrics and Experiment Setup . . . . . . . . . . 22.2 Performance Improvement . . . . . . . . . . . . . . . . . . . . 23.2.1 Data Transmission Time . . . . . . . . . . . . . . . . . 23.2.2 Live-Page Copyings . . . . . . . . . . . . . . . . . . . 25.3 Extra RAM Consumption . . . . . . . . . . . . . . . . . . . . 26.4 Remark: Wear-Leveling . . . . . . . . . . . . . . . . . . . . . 28hapter 5 CONCLUSION AND FUTURE WORK . . . . . . . . . . 30eferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3