Recovery Techniques to Improve File System

RECOVERY TECHNIQUES TO IMPROVE FILE SYSTEM RELIABILITY Swaminathan Sundararaman We implement selective restart and resource reservation for commodity file systems to improve their reliability. Selective restart allows file systems to quickly recover from failures; resource reservation enables file systems to avoid certain failures altogether. Together they enable a new class of more robust and reliable file systems to be realized. In the first part of this dissertation (on selective restart), we develop Membrane, a generic framework built inside the operating system to selectively restart kernellevel file systems. Membrane allows an operating system to tolerate a broad class of file system failures and does so while remaining transparent to running applications; upon failure, the file system restarts, its state is restored, and pending application requests are serviced as if no failure had occurred. We also develop Re-FUSE, a generic framework designed to restart user-level file systems upon failures. ReFUSE monitors the user-level file-system and on a crash restarts the file system and restores its state; the restart process is completely transparent to applications. We evaluate both Membrane and Re-FUSE, and show, through experimentation, that both of these frameworks induce little performance and space overhead and can tolerate a wide range of crashes with minimal code change. In the second part of the dissertation (on resource reservation), we develop Anticipatory Memory Allocation (AMA), a technique that uses static analysis to simplify recovery code dealing with memory-allocation failures. AMA determines the memory requirements of a particular call into a file system, and then pre-allocates said amount immediately upon entry; subsequent allocation requests are serviced from the pre-allocated pool and thus guaranteed never to fail. We evaluate AMA by transforming Linux ext2 file system into a memory-failure robust version of itself (called ext2-mfr). Experiments reveal that ext2-mfr avoids memory-allocation failures successfully while incurring little space and time overheads.