vStream: Virtual Stream Management for Multi-streamed SSDs

Recently, multi-streamed SSDs have been proposed to reduce the cost of garbage collection in NAND flash-based SSDs. In multi-stream SSDs, application developers can control data placement within the SSD by specifying a stream ID along with the write command. However, commercial SSDs support only a small number of streams due to the device's limitation in hardware resources. This makes it difficult to fully utilize the benefit of the multi-streamed SSDs.

In this paper, we propose a new concept of virtual streams (vStreams) for the multi-streamed SSDs. vStreams allow application developers to manage a sufficient number of streams regardless of the physical streams supported by the device. We also present novel mechanisms to monitor the lifetime of each stream with a negligible memory overhead and to map one or more vStreams into a physical stream at run time. Our evaluations with RocksDB show that the proposed vStream SSD improves the throughput by 70% compared to the legacy SSD with no stream support.