LSDM: Improving the Performance of Mobile Storage with a Log-Structured Address Remapping Device Driver

Abstract—Mobile devices use low-cost SSDs such as microSD cards and eMMC devices for persistent data storage. However, The controllers of low-cost SSDs are optimized for reads and for sequential writes and they perform poorly under random writes. In this paper, we show that it is possible to overcome this limi-tation using a novel device driver on the host. Our driver, called LSDM, uses design techniques normally used in the firmware (FTL) of high-end SSD to transform random writes to sequential ones. Our driver is a generic kernel module that interfaces an existing file system to the block device that represents the SSD, transforming the arbitrary read/write request sequence of the file system to a sequence with long streams of sequential writes; even low-cost SSDs perform well on such sequences. The use of an existing unmodified file system allows users and administrators to benefit from mature, feature-complete file systems. Our prototype implementation speeds up all filebench workloads used, by up to a factor of 6. Our experiments show that a flash-friendly file system that generates long streams of sequential writes delivers performance that is similar to a conventional file system mounted on LSDM. The high complexity of a completely new file system, relative to the simplicity of LSDM, favors our solution. I