Hotness-Aware Runtime Zone Reset and Reallocation Optimizations for ZNS SSDs

ZNS SSDs reduce address mapping, garbage collection (GC), and over-provisioning costs by organizing storage into sequential-write zones. ZenFS is a file system specifically designed for ZNS SSDs. Runtime zone reset is a key operation in ZenFS, allowing zones to be reclaimed during execution and thereby reducing the need for GC. However, research on how to efficiently use this mechanism remains limited. Specifically, ZenFS uses a fixed reset timing for all zones regardless of their varying hotness, hence failing to optimize write amplification and space utilization. In this work, we propose a hotness-aware optimization method that comprises an adaptive timing control mechanism for runtime zone resets and a dynamic zone reallocation mechanism. The key idea is to adaptively control each zone’s reset timing based on its hotness and the SSD’s available space. Additionally, when space is sufficient, the reallocation mechanism allows zones with fully invalidated data to remain in use, avoiding unnecessary resets. The zone-level timing control optimizes space availability and reduces write amplification in ZNS SSDs. Specifically, hot zones benefit from extended service time before reset, improving space utilization, while cold zones are reset more promptly, minimizing GC-induced erasures and data migration. Moreover, the dynamic zone reallocation mechanism extends the lifetime of zones with invalidated data when space permits, further reducing erasures. Experimental results show that the proposed method significantly reduces the zone reset count by average factors of 1.72 × and 1.57 × in comparison to the traditional and latest approaches, respectively.