An Adaptive Zone-Grouping Scheme Enabling General-Purpose File Systems on ZNS SSDs

Zoned namespace solid state drives (ZNS SSDs) provide superior capacity and life span compared to conventional namespace (CNS) SSDs at the same cost. Especially, a small-zone ZNS SSD can achieve a low write amplification factor (WAF) and performance isolation among I/O streams by providing the host with finer-grained control of the SSD's flash chips than the large-zone counterpart. To maximize these advantages, multiple zones in a small-zone SSD should be grouped and operated simultaneously. A ZNS-aware file system encapsulates the ZNS interface and transforms a ZNS SSD into a general-purpose storage to the host layer. However, the current ZNS-aware file systems were designed for the large-zone ZNS SSDs, and thus lack the zone group management feature. This paper proposes a dynamic zone group management scheme for ZNS-aware file systems that dynamically adjusts the number of zone groups in accordance with the workload characteristics and the size of each zone group to achieve high performance at a low WAF. The proposed scheme was implemented in the F2FS. Our evaluation with FIO, Filebench and db_bench showed that, across all cases, the proposed scheme improved the performance by up to 71.2% while reducing the WAF by 29.8% in comparison to the static zone grouping scheme.