The Zoned Namespace (ZNS) SSD is an innovative technology that aims to mitigate the block interface tax associated with conventional SSDs. However, constructing a RAID system using ZNS SSDs presents a significant challenge in managing partial parity for incomplete stripes. Previous research permanently logs partial parity in a limited number of reserved zones, which not only creates bottlenecks in throughput but also exacerbates write amplification, thereby reducing the device's lifetime. We refer to these inefficiencies as the partial parity tax. In this paper, we present ZRAID, a software ZNS RAID layer that leverages the newly added Zone Random Write Area (ZRWA) feature in the ZNS Command Set, to alleviate partial parity tax. ZRWA enables in-place updates within a confined area near the write pointer. ZRAID temporarily stores partial parity within the ZRWA of data zones. Thus, partial parity writes are distributed across multiple data zones, effectively eliminating throughput bottlenecks. Furthermore, any expired partial parity in the ZRWA is overwritten by subsequent data, avoiding unnecessary flash writes. With the introduction of ZRWA, ZRAID can leverage general schedulers, overcoming the queue depth limitations of ZNS-compatible schedulers. Our evaluation with actual ZNS SSDs demonstrates a significant improvement in write throughput: up to 34.7% in the fio microbenchmark, and an average of 14.5% in db_bench on RocksDB, along with up to a 1.6x reduction in flash write amplification.

@inproceedings{KimJ025,
  title = {ZRAID: Leveraging Zone Random Write Area (ZRWA) for Alleviating Partial Parity Tax in ZNS RAID},
  author = {Minwook Kim and Seongyeop Jeong and Jin-Soo Kim},
  booktitle = {ASPLOS},
  year = {2025},
  doi = {10.1145/3669940.3707248}
}