SOS: Software-based out-of-order scheduling for high-performance NAND flash-based SSDs

We propose an efficient software-based out-of-order scheduling technique, called SOS, for high-performance NAND flash-based SSDs. Unlike an existing hardware-based out-of-order technique, our proposed software-based solution, SOS, can make more efficient out-of-order scheduling decisions by exploiting various mapping information and I/O access characteristics obtained from the flash translation layer (FTL) software. Furthermore, SOS can avoid unnecessary hardware-level operations and manage I/O request rearrangements more efficiently, thus maximizing the multiple-chip parallelism of SSDs. Experimental results on a prototype SSD show that SOS is effective in improving the overall SSD performance, lowering the average I/O response time by up to 42% over a hardware-based out-of-order flash controller.