Centaur: A Novel Architecture for Reliable, Low-Wear, High-Density 3D NAND Storage

Due to the high density storage demand coming from applications from different domains, 3D NAND flash is becoming a promising candidate to replace 2D NAND flash as the dominant non-volatile memory. However, denser 3D NAND presents various performance and reliability issues, which can be addressed by the 3D NAND specific full-sequence program (FSP) operation. The FSP programs multiple pages simultaneously to mitigate the performance degradation caused by the long latency 3D NAND baseline program operations. However, the FSP-enabled 3D NAND-based SSDs introduce lifetime degradation due to the larger write granularities accessed by the FSP. To address the lifetime issue, in this paper, we propose and experimentally evaluate Centaur, a heterogeneous 2D/3D NAND heterogeneous SSD, as a solution. Centaur has three main components: a lifetime-aware inter-NAND request dispatcher, a lifetime-aware inter-NAND work stealer, and a data migration strategy from 2D NAND to 3D NAND. We used twelve SSD workloads to compare Centaur against a state-of-the-art 3D NAND-based SSD with the same capacity. Our experimental results indicate that the SSD lifetime and performance are improved by 3.7x and 1.11x, respectively, when using our 2D/3D heterogeneous SSD.