MNK: Configurable Hybrid Flash Translation Layer for Multi-Channel SSD

Abstract

For multi-channel Solid State Disks (SSDs), hybrid Flash Translation Layer (FTL) schemes were developed for increasing I/O parallelism and reducing garbage collection overhead. However, they still suffer from the high read and write latency, block thrashing problem, and load balancing problem. In order to overcome these problems, we design a configurable hybrid FTL, called MNK. MNK consists of a configurable mapping scheme, recycling log block scheme, and load balancing scheme. By applying the configurable mapping scheme, we can not only exploit the multi-channel architecture of SSD for I/O parallelism but also achieve bounded read/write latency with low garbage collection overhead by controlling the number of modules in striping (M), the number of logical blocks in a group (N), and the maximum allowed log blocks for a group of N logical blocks (K), respectively. In the recycling log block scheme, we can achieve low garbage collection overhead by reducing erase operations. Through the load balancing scheme, we make the erase counts of multiple modules even, thereby increasing the lifetime of SSD. In order to evaluate the performance of the proposed MNK scheme, we use a trace-driven simulator. MNK finally reduces read/write latency by up to 81% compared to previous hybrid FTL schemes such as MCSplit and SubGroup.