Apas: An Application Aware Hybrid Storage System Combining SSDs and SWDs

Shingled write disk (SWD) is a new kind of HDD, which increases areal density by adopting SMR technology. In the hybrid storage system consisting of SSDs and SWDs, there are some special characteristics such as large performance gap between SSDs and SWDs. In this paper we explore how to efficiently combine the advantages of SSDs and SWDs together. We propose Apas, an application aware hybrid storage system combining SSDs and SWDs, where SSDs are used as nonvolatile cache and SWDs work as lower level storage. In Apas we propose a cache partitioning policy to divide the cache space according to the application's characteristics. To mitigate the write amplification problem in SWDs, we first classify data bands in the SWDs into five types according to the distribution of valid data in the bands, and then design a new garbage collection policy combining the aggressive data cleaning and lazy data cleaning together according to the detected idle time and the five types of bands. Experiments are carried out and the results show that Apas has good performance.