SJM: an SCM-based journaling mechanism with write reduction for file systems

Considering the unique characteristics of storage class memory (SCM), such as non-volatility, fast access speed, byte-addressability, low-energy consumption, and in-place modification support, we investigated the features of over-write and append-write and propose a safe and write-efficient SCM-based journaling mechanism for a file system called SJM. SJM integrates the ordered and journaling modes of the traditional journaling mechanisms by storing the metadata and over-write data in the SCM-based logging device as a write-ahead log and strictly controlling the data flow. SJM writes back the valid log blocks to the file system according to their access frequency and sequentiality and thus improves the write performance. We implemented SJM on Linux 3.12 with ext2, which has no journal mechanisms. Evaluation results show that ext2 with SJM outperforms ext3 with a ramdisk-based journaling device while keeping the version consistency, especially under workloads with large write requests.