SCJ: Segment Cleaning Journaling for Log-Structured File Systems

The append-only write scheme of the log-structured file system (LFS), which does not permit in- place updates, is suitable for flash memory. Therefore, LFSs have been adopted to manage various flash-memory-based storage systems. However, LFSs amplify user write requests owing to segment cleaning and frequent metadata write operations. Hence, the IO performance is degraded and the life span of the flash memory is reduced. In particular, when each segment cleaning invokes checkpointing to store dirty metadata modified via block relocation, irrelevant dirty metadata are written by the checkpointing operation, and the metadata write overhead occupies a significant proportion of the segment cleaning latency. Hence, we propose segment cleaning journaling (SCJ), which logs the block relocation information of segment cleaning at a specific journal area without invoking checkpointing. We implemented and evaluated the proposed SCJ by modifying F2FS. Experimental results show that SCJ can improve file system performance by 1.13–1.63 times compared with normal segment cleaning.