Unaligned Access Optimization with Request-based Mapping Scheme for Solid-state Drives

Flash-based solid-state drives (SSDs) have become increasingly popular in a variety of storage systems due to their impressive performance capabilities. However, due to the basic I/O unit asymmetry between the host systems and underlying storage devices, SSDs need to handle a large number of unaligned access which can lead to severe write amplification and page fragmentation, thereby degrading the I/O performance, space utilization and endurance of SSDs. For mitigating the negative effects caused by unaligned access, this paper proposes a request-based address mapping scheme for SSDs to map the request data to the minimum number of flash pages based on the request size, while a novel compression scheme considering the characteristics of SSDs is applied to further eliminate the page fragmentation that remains after mapping. Simulation tests on several realistic disk traces show that our proposal can improve the I/O performance by 31.7% and reduce page fragments by 25.4% on average, compared to state-of-the-art methods.