Turn Waste Into Wealth: Alleviating Read/Write Interference in ZNS SSDs

The emerging NVMe Zoned Namespace (ZNS) solid-state drive (SSD) is built on high-density NAND flash memories. As write latency is much longer than read latency in NAND flash memories, the read performance of ZNS SSD is subject to the chip-blocking writes. However, current works on alleviating read/write interference are usually designed for traditional SSDs, which cannot be applied to the ZNS SSD due to its unique constraints. In this work, we find that many zones marked as full actually have some empty and wasted spaces, to which we refer as idle space. We back up popular read data with idle space. To minimize the overhead, we leverage device-side information to ensure that only one backup is needed. Secondly, we propose an I/O scheduling method through request splitting to ensure that the sole backup is not blocked by any writes and can always serve blocked reads. Experiments show that when compared to the current ZNS SSDs, our work significantly improves average read response time and read tail latency of 99^th and 99.9^th percentile by up to 44.28%, 50.09%, and 46.68%. Moreover, our work prevails over the read-prioritizing scheme on read performance and write tail latency.