Improving the performance and lifetime of TLC SSD by leveraging flash level disparities

Because more and more applications need high performance yet large capacity storages, solid state drives (SSD) based on triple level cell (TLC) flash memory have been playing an essential role in the storage systems. Although significantly increasing storage capacity, TLC flash memory severely degrades the raw reliability and thus drastically decreases lifetime. However, after evaluating real flash chips, the researchers have shown that worn-out blocks can be reused in flash lifespan. This paper suggests a novel flash translation layer (FTL) called graceful degradation flash translation layer (GD-FTL) by downgrading worn-out TLC blocks to SLC blocks to extend lifetime and improve performance of SSDs. We further propose to store hot data on SLC-mode blocks and proactively conduct mode transitions to meet predefined service level objects. Four real workloads are used to evaluate the proposed GD-FLT. Experiment results show that GD-FLT can improve the performance and reduce write amplification of solid state drives.