A Cost-Efficient NVM-Based Journaling Scheme for File Systems

Modern file systems employ journaling techniques to guarantee data consistency in case of unexpected system crashes or power failures. However, journaling file systems usually suffer from performance decrease due to the extra journal writes. Moreover, the emerging non-volatile memory technologies (NVMs) have the potential capability to improve the performance of journaling file systems by being deployed as the journaling storage devices. However, traditional journaling techniques, which are designed for hard disks, fail to perform efficiently in NVMs. In order to address this problem, we propose an NVM-based journaling scheme, called NJS. The basic idea behind NJS is to reduce the journaling overhead of traditional file systems while fully exploiting the byte-accessibility characteristic, and alleviating the relatively slow write and endurance limitation of NVM. Our NJS consists of three major contributions: (i) In order to minimize the amount of journal writes, NJS only needs to write the metadata of file systems and over-write data to NVM as write-ahead logging, thus alleviating the relatively slow write and endurance limitation of NVM. (ii) We propose a novel journaling update scheme in which the journaling data blocks can be updated in the byte-granularity based on the difference of the old and new versions of journal blocks, thus fully exploiting the unique byte-accessibility characteristic of NVM. (iii) NJS includes a garbage collection mechanism that absorbs the redundant journal updates, and actively delays the checkpointing to the file system. Evaluation results show the efficiency and efficacy of NJS. For example, compared with original Ext4 with a ramdisk-based journaling device, the throughput improvement of Ext4 with our NJS is up to 137.1%.