A workload-aware-design of 3D-NAND flash memory for enterprise SSDs

Solid-state drives (SSDs) have a growing trend of replacing hard disk drives (HDDs) in large computing systems to meet the requirements of power and space. Data in SSD are stored in NAND flash memory cells. Since 2-dimensional (2D) scaling is facing various limitations, 3D-NAND flash memory architectures have been proposed to maintain the trend of bit density increase and bit cost reduction, which prefers large block sizes and page sizes. However, overly large block and page sizes flash memory harm the throughput of NAND flash devices. The actual page size and block size of the NAND flash memory product are as small as 8KB and 2MB respectively to avoid the performance degradation. Alternatively, emerging nonvolatile memory devices named storage class memories (SCMs) feature in high speed, low power consumption and high endurance. By combining SCM, large block sizes and page sizes, required especially for the 3D-NAND flash device case, are acceptable for SCM/NAND flash hybrid SSD. In this paper, a workload-aware NAND organization design is investigated for enhancing the performance of both SSD with only NAND flash memory and SCM/NAND flash hybrid SSD. From the experimental results, a 16MB NAND block size that corresponds to 512 layers and 16KB page size in a 512Gbit P-BiCS 3D-NAND flash memory can be acceptable for applications like relational database and financial online transaction processing. Additionally, a large NAND flash page size of 512KB is also acceptable for the firewall/web proxy, relational database and project directories applications. With SCM, the acceptable page and block sizes of the 3D-NAND flash memory can be magnified up to 64-times and 4-times, respectively, compared with the conventional SSD composed of only NAND flash memory.