RMW-F

Shingled Magnetic Recording (SMR) disks have been proposed as a high-density, non-volatile media and precede traditional hard disk drives in both storing capacity and cost. However, the intrinsic characteristics of SMR disks raise a major performance challenge named read-modify-write operations (RMWs) that are time-consuming and can significantly degrade the overall system performance. Current designs of SMR disks usually adopt a persistent cache to alleviate the negative effect brought by RMWs and the cache is used as a first-level cache to buffer all the incoming writes of the whole SMR storage system. In this paper, we propose to change the functionality of the cache, that is, the cache will no longer serve as a first-level cache like previous. Incoming data are distinguished according to their different write-back behavior and those data which will incur RMWs will be left in our built-in NAND flash cache called RMW-free Cache (RMW-F) to eliminate the need of RMWs. Besides, RMW-F improves the cleaning efficiency by a model that takes both write-back cost and data popularity into considerations. Our experimental results show that RMW-F can achieve both system performance and cleaning efficiency improvements.