Breathing new life into compression: Resolving the dilemma of LFS with compression on flash storage

State-of-the-art storage systems have widely adopted log-structured file systems (LFS) with unique append–write capability, making them ideal for supporting compression. Compression is a recognized way of reducing data-occupied space and extending the lifetime of flash. However, implementing file system-level compression faces a dilemma that hampers its adoption. Two significant issues are responsible for this. Firstly, the software stack overhead resulting from compression is costly. Due to its location on the critical path for reads and writes, compression will block the user's I/O requests. Secondly, compressing as much space as possible to enjoy the benefits of compression in terms of space will inevitably introduce compression overhead. This paper proposes a novel no-critical path compression scheme that significantly eliminates compression's current dilemma. The basic idea is to perform non-critical path compression, minimizing the performance impact and maximizing the benefits of compression in space by disengaging compression from the critical paths of reads and writes. To achieve this, a critical path detachment scheme is first proposed to detach the compression from the critical path based on the properties of the non-critical path compression. Furthermore, a contention-avoiding scheduling scheme is proposed to minimize the impact on CPU costs. Finally, a reserve space (RS)-oriented allocation scheme is proposed to exploit the benefits of compression in space to optimize the cleaning cost of LFS. Through careful design and evaluation on a real platform, we demonstrate that the proposed scheme, NCPC, achieves encouraging performance and lifetime optimizations compared to state-of-the-art solutions.