Hybrid solid-state disks: combining heterogeneous NAND flash in large SSDs

TLDR

NAND‑flash‑based SSDs are increasingly used in embedded computers to replace power‑hungry disks. The study proposes a hybrid SSD that combines MLC and SLC flash to leverage each type’s strengths and mitigate their weaknesses. The design addresses data placement and wear‑leveling challenges across heterogeneous NAND flash components. Experimental results show that adding 256 MB of SLC to a 20 GB MLC array yields a 4.85× faster average response, 17 % higher throughput, 14 % lower energy use, and only a 2 % cost increase compared to a pure MLC SSD.

Abstract

NAND-flash-based SSDs (solid-state disks) are recently used in embedded computers to replace power-hungry disks. This paper presents a hybrid approach to large SSDs, which combines MLC flash and SLC flash. The idea is to complement the drawbacks of the two kinds of NAND flash with each other's advantages. The technical issues of the design of a hybrid SSD pertain to data placement and wear leveling over heterogeneous NAND flash. Our experimental results show that, by adding a 256 MB SLC flash to a 20 GB MLC-flash array, the hybrid SSD improves over a conventional SSD by 4.85 times in terms of average response. The average throughput and energy consumption are improved by 17 % and 14%, respectively. The hybrid SSD is only 2% more expensive than a purely MLC-flash-based SSD, for which the extra cost is limited and very rewarded.