State-based die binding for enhancing SSD internal parallelism

Solid state drives (SSDs) implement large capacity, high performance storage devices by connecting multiple NAND flash memory chips in parallel using multiple channels. Channels can transfer data simultaneously, and each NAND package is composed of multiple dies, which can independently perform NAND operations such as read, write, and erase. Therefore, maximizing the parallel processing capability inside the SSD is important for performance improvement. However, the existing logical address based die binding policy has a disadvantage in that it can concentrate requests only on specific dies, and the existing dynamic binding policy that considers the state of each die has a limitation that it can be used only for the SSD where each die is connected with a dedicated channel. Therefore, in this paper, we propose a dynamic die binding policy that considers both channel state and die state for enhancing internal parallelism of general SSDs where multiple dies share a channel. The performance evaluation results show that the proposed policy shows a performance improvement of more than 20% over the logical address based static binding policy.