ECAM: An Efficient Cache Management Strategy for Address Mappings in Flash Translation Layer

Solid State Drives (SSDs) have been widely adopted in both enterprise and embedded storage systems with the great improvement in NAND flash memory technology. With the growing size of NAND flash memory, how to keep the most active address mappings be cached in limited on-flash SRAM is crucial to a Flash Translation Layer (FTL) scheme, that plays an important role in managing NAND flash. In this paper, we propose an efficient cache management strategy, called ECAM, to enhance the capability of caching page-level address mappings in demand-based Flash Translation Layer. In ECAM, we optimize the structure of Cached Mapping Table (CMT) to record multiple address mappings with consecutive logical page numbers and physical page numbers in just one mapping entry, and propose another two tables, Cached Split Table (CST) and Cached Translation Table (CTT). CST can cache the split mapping entries caused by the partial updates in CMT and CTT is used to reduce the overhead of address translation for large number of sequential requests. By the cooperation of CMT, CST and CTT, ECAM implements an efficient two-tier selective caching strategy to jointly exploit the temporal and spatial localities of workloads. The simulation on various realistic workloads shows that ECAM can improve the cache hit ratio and reduce the number of expensive extra read/write operations between SRAM and flash efficiently.