Optimizations of LFS with slack space recycling and lazy indirect block update

Abstract

Even though the Log-structured File System (LFS) has elegant concept for superior write performance, it suffers from cleaning overhead. Specifically, when file system utilization is high and the system is busy, write performance of LFS degenerates significantly. Also, cascading update of meta-data triggered by modification of file data decreases LFS performance further. To overcome the performance drawbacks of LFS, we propose two schemes, namely Slack Space Recycling (SSR) and Lazy Indirect Block Update (LIBU). The SSR scheme writes modified data to invalid areas of used segments when on-demand cleaning is inevitable to serve incoming write requests. Also, the LIBU scheme accumulates meta-data update in memory beyond multiple segment writes without compromising consistency so as to decrease total amount of writes. From various experimental results, we observe significant performance improvements when employing the SSR and LIBU schemes for a wide utilization range.