Zebra: Efficient Redundant Array of Zoned Namespace SSDs Enabled by Zone Random Write Area (ZRWA)

Zoned Namespace (ZNS) SSDs have emerged as a promising solution for eliminating device-level garbage collection and achieving predictable performance through the zone abstraction, which supports append-only writes. However, integrating ZNS SSDs into RAID configurations presents challenges, particularly concerning partial parity updates (PPUs) due to the no-overwrite property of ZNS SSDs. Existing solutions introduce dedicated metadata zones to manage PPUs, but these zones become performance bottlenecks, especially under high PPU workloads.In this paper, we introduce Zebra, a novel architecture for ZNS RAID that leverages the Zone Random Write Area (ZRWA) feature of modern ZNS SSDs. Our key insight is that the SSD’s write buffer (or ZRWA) in front of each zone is ideal for PPUs that exhibit a repeated sequential overwrite I/O pattern. By ensuring that the parity chunk fits within the ZRWA window, Zebra enables efficient PPUs within the ZRWA. Combined with a set of techniques, Zebra ensures both high performance and reliability. We evaluate Zebra on both large-zone and small-zone ZNS SSDs, two typical ZNS models. Our experiments with micro and application benchmarks show that Zebra improves the throughput by 1.1×-4.2× compared to RAIZN, a state-of-the-art ZNS RAID system.