SHRD: Improving Spatial Locality in Flash Storage Accesses by Sequentializing in Host and Randomizing in Device

Recent advances in flash memory technology have reduced the cost-per-bit of flash storage devices, thereby enabling the development of large-capacity SSDs. However, two major concerns arise in designing SSDs. The first is the poor performance of random writes, and the second is the large size of the internal DRAM of an SSD. Although the previously proposed demand map loading technique can reduce the required DRAM size, the technique aggravates the poor random performance. We propose a novel address reshaping technique called sequentializing in host and randomizing in device (SHRD), which transforms random write requests into sequential write requests by assigning the address space of the reserved log area in the SSD. SHRD can restore the sequentially written data to the original location without requiring explicit copy operations by utilizing the address mapping scheme. We implement SHRD in a real SSD device and demonstrate the improved performance resulting from SHRD for various workloads1.