2R: Efficiently Isolating Cold Pages in Flash Storages

NAND flash-based solid-state drives have revolutionized storage solutions in resource-restrictive electronics owing to their compact size, low power consumption, and high shock resistance. However, they face limitations such as asymmetrical read, write, and erase operations, leading to write amplification (WA), decreased performance, and shorter lifespan. This paper introduces clustering sequential writes and cold isolation (CSWCI), a novel data placement scheme that addresses two critical challenges: identifying sequential writes hidden within random input/output streams and efficiently migrating cold pages. CSWCI employs logical address-based clustering to detect sequential patterns, enhancing spatial locality and reducing random writes. Additionally, it accurately isolates frozen pages that have not been used recently and are not expected to be used again during garbage collection, thus minimizing unnecessary migrations and WA. Unlike conventional methods, CSWCI optimizes memory usage, aligning with the low power consumption requirement of mobile devices such as smartphone and tablet PC. Experimental results demonstrate a maximum 33% reduction in valid page copies, which typically worsens WA compared to existing schemes, indicating improved performance and durability.