Minimizing consistency-control overhead with rollback-recovery for storage class memory

To guarantee system reliability, consistency-control scheme, such as journaling, is widely used in modern computing environments. However, existing consistency-control schemes negatively affect system performance because they frequently issue write commands to the storage device in order to guarantee data consistency and durability. Especially, when a storage class memory (SCM) is attached to memory bus as storage device, existing consistency-control schemes should be revisited because the buffer cache layer can be potentially eliminated. In this paper, we propose a novel consistency-control scheme, called MinL2R, which guarantees system reliability in the systems that have SCM device attached to memory bus. MinL2R significantly reduces the amount of backup data by performing data logging that records the original data related to updates at the granularity of a byte. In addition, MinL2R supports pointer logging in order to further reduce the logging overhead, when the size of updates is larger than the size of half of a block. To evaluate our scheme, we implemented the MinL2R prototype with SCM-aware file systems, such as BPFS and Shortcut-JFS. Then, we compared the performance of MinL2R against different file systems including Ext4, BPFS, and Shortcut-JFS, by using several I/O benchmarks. The experimental results clearly show that MinL2R outperforms by up to 286%, 291%, and 395% on BPFS, Shortcut-JFS, and the Ext4 file system with journal mode, respectively.