LOONG: Utilizing Long-Stride Reprogramming to Enhance the Performance of SSDs

NAND flash-based SSDs enforce strict sequential page programming within blocks, primarily due to reliability constraints. However, enabling reprogramming of pages after initial writes could unlock significant optimization opportunities, such as accelerating valid page movement during garbage collection or program operations. Toward this objective, prior work has explored reprogramming. Nevertheless, its effort faces a critical limitation: reprogramming is restricted to a small subset of wordlines per block (i.e., stride), rather than extending to all WLs per block. In this work, we advance beyond this constraint with LOONG, a method that expands the reprogramming stride to encompass entire blocks. LOONG introduces a long-stride reprogram operation, which spatially decouples programming steps. First, all WLs in a block undergo sequential programming in SLC mode to maximize performance. These pages are then uniformly reprogrammed to TLC mode, preserving storage capacity. LOONG requires no hardware modifications and can be deployed solely via firmware updates. We evaluate LOONG's efficiency with two case studies: GC acceleration and program operation optimization. Experimental results demonstrate average latency is reduced by 37.5% and 18.1%, respectively, in these two scenarios.