FJS: Fine-grained Journal Store

Journaling has been a popular reliability tool for file systems. However, journaling may involve writing updates twice, once to the journal, and once to potentially random update locations. The journal granularity tends to be coarse, leading to more bytes written than necessary. We introduce Fine-grained Journal Store (FJS). Finegrained Journal Store uses the journal as the final storage location for updates, thus eliminating double and random writes. Fine-grained journaling units are utilized to reduce the number of bytes written compared to the number of bytes updated. To limit the memory overhead of tracking small updatable units, FJS uses a range-based lookup table. In addition, FJS reuses existing journaling constructs to avoid the need for additional byte-addressable NVM storage devices. We extended ext4 and jbd2 to prototype FJS. Our results show that FJS can outperform ext4 by up to 15x and reduce the write amplification of common metadata types by up to 5.8x. CCS Concepts •Information systems~Record storage systems