Last block logging mechanism for improving performance and lifetime on SCM-based file system

The emerging Storage Class Memory, which offers characteristics of byte-addressability, persistence, and low power consumption, will be expected to replace memory/storages. A new file system is required in this environment. In the design of file systems, data consistency is one of the most important issues that should be taken into account. To do this, most file systems exploit journaling or shadow paging for the consistency. Shadow paging employs copy-on-write for the consistency. However, it incurs many copy over- heads. In order to relieve these problems, BPFS proposed a short-circuit shadow paging. But, in our experiments, we showed that it incurs many copy-on-write blocks as ever. In this paper, we propose a last block logging mechanism for improving the performance and the lifetime of SCM-based file system, by reducing copy-on-write blocks considerably. Our approach is to store the only changed contents to the available space of the last block, instead of performing copy- on-write on the entire block. Also, our approach updates the address of the last block and maintains the information on the logged data in order to ensure the data consistency. SQLite benchmark shows that the proposed mechanism reduces the overall elapsed time by 14% and the written data amount up to 72%, compared to the mechanism of BPFS.