Parallel Aware Hybrid Solid-State Storage

Abstract

Compared with tradition disk, NAND Flash has advantages of higher performance and shock resistance. But before write, NAND Flash must erase the old messages. That why NAND Flash based Solid State Disks (SSDs) always use the log-based schemes to improve the performance. Compared with NAND Flash, Phase Change Memory (PCM) has higher write performance, longer lifetime, and can update in-place, but its cost is high and capacity is low. So, in PCM and NAND Flash hybrid SSD, PCM is always used as log region, such as In-Page Logging-based (hybrid-IPL) SSD. The log-based SSD incurs a large number of merge operations. The cost of merge operation is very high because it involves many read, write operations, as well as an erase operation. So, how to reduce the cost of merge operations is the critical challenge to log-based hybrid (PCM and flash) SSD. In this paper, we propose a new merge scheme in PCM and NAND Flash hybrid SSD, called Parallel aware hybrid In-Page Logging-based (P-aware-IPL) SSD. This scheme can exploit the die-level and plane-level parallelism of flash. Leveraging these two levels of parallelism, the cost of full merge is significantly reduced compared with that of hybrid-IPL SSD scheme and there is no other additional overhead in our algorithm. Experiment results have shown that the proposed P-aware-IPL reduces the flash write and erase operations by up to 10 % and average response time by up to 22 % against the hybrid-IPL scheme.