Open-Channel SSD and Zoned Namespace (ZNS): Architecture, Benefits, and Performance with RocksDB and ZenFS

01. Origin: Open-Channel

Traditional NVMe SSDs expose a generic block interface that hides the underlying NAND layout, limiting performance because the firmware‑based Flash Translation Layer (FTL) cannot be optimized for specific workloads. Open‑Channel SSDs expose the NAND physical layout to the host, giving the host control over data placement, I/O scheduling, wear‑leveling, and garbage collection, which improves QoS, latency predictability, and enables true I/O isolation.

02. Evolution: ZNS

Zoned Namespace (ZNS) builds on Open‑Channel concepts by defining fixed‑size zones within a namespace that must be written sequentially. This standardizes the interface, reduces write amplification, simplifies garbage collection, and allows the host to manage zones directly, resulting in more efficient GC, predictable latency, lower over‑provisioning, and reduced DRAM usage.

03. Case Study: Shannon Systems SP4

The SP4 ZNS SSD from Shannon Systems supports up to eight open zones, 8–9 GB per zone, and an 8 TB total capacity. Benchmarks using FIO in ZBD mode show that SP4 achieves comparable sequential read performance to a traditional P5510 SSD while delivering 26 % higher sequential write throughput and 16 % faster random reads.

04. ZNS Ecosystem: RocksDB + ZenFS

RocksDB, a flash‑aware key‑value store, writes data sequentially and avoids in‑place updates, making it a good match for ZNS. ZenFS, a user‑space file system plugin for RocksDB, manages ZNS zones via libzbd, providing direct zone allocation and I/O. Performance tests demonstrate that RocksDB + ZenFS on ZNS SSDs can double write throughput and cut 99.99 % read latency to one‑quarter of that on traditional SSDs.

05. Outlook

Future work includes reducing space amplification caused by stale zones, implementing copy‑back data movement, supporting variable‑size zones, and exposing zone APIs through kernel drivers or libraries like xNVMe to enable tighter integration with databases and file systems, further improving latency and QoS for enterprise storage.