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

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.