PCFTL: A Plane-Centric Flash Translation Layer Utilizing Copy-Back Operations

A software module named flash translation layer (FTL) running in the controller of a flash SSD exposes the linear flash memory to the system as a block storage device. The effectiveness of an FTL significantly impacts the performance and durability of a flash SSD. In this research, we propose a new FTL called PCFTL (Plane-Centric FTL), which fully exploits plane-level parallelism supported by modern flash SSDs. Its basic idea is to allocate updates onto the same plane where their associated original data resides on so that the write distribution among planes is balanced. Furthermore, it utilizes fast intra-plane copy-back operations to transfer valid pages of a victim block when a garbage collection occurs. We largely extend a validated simulation environment called SSDsim to implement PCFTL. Comprehensive experiments using realistic enterprise-scale workloads are performed to evaluate its performance with respect to mean response time and durability in terms of standard deviation of writes per plane. Experimental results demonstrate that compared with the well-known DFTL, PCFTL improves performance and durability by up to 47 and 80 percent, respectively. Compared with its earlier version (called DLOOP), PCFTL enhances durability by up to 74 percent while delivering a similar I/O performance.