Analysis and Evolution of a Journaling File System

Abstract

We present measurements and analysis of the Linux ext3 file system. We develop and apply a novel analysis method known as semantic block-level analysis (SBA), which examines the low-level block stream that a file system generates in order to understand its behavior under a series of controlled workloads. We use SBA to evaluate the strengths and weaknesses of the ext3 design and implementation; in comparison to standard benchmarking approaches, SBA enables us to understand why the file system behaves in a certain way, knowledge that is usually only available to the file system developers. We then develop and apply a new complementary technique known as semantic trace playback (STP) to evaluate the effect of different possible changes to the file system. In contrast to the cumbersome and time-consuming process of changing the file system implementation directly, STP enables us to rapidly gauge the potential benefits of a given file system modification without the heavy investment in implementation effort. Using STP, we propose and assess various modifications to the base ext3 implementation.