Optimizing F2FS performance with the inter-zone parallelism in small-zone ZNS SSDs

ZNS SSDs are usually equipped with small zones to improve space utilization. However, a small zone is mapped to a limited number of chips, which results in a limited parallelism of the chips. Moreover, F2FS ignores the utilization of the inter-zone parallelism, resulting in an inability to fully utilize the chip parallelism of a ZNS SSD. On the one hand, inter-zone parallelism is rarely utilized when the request size of workloads is smaller than that of a zone. On the other hand, the inter-zone parallelism utilization is further limited by the inter-zone interference.

To address these issues, this paper proposes a full-parallelism zone allocation and writing strategy for F2FS, termed FPZone. The core idea is to allow each data log of F2FS to be written in parallel to multiple zones mapped to different chips to improve the inter-zone parallelism. First, a parallel zone grouping method is proposed to group zones mapped to different chips into multiple parallel zone groups. Then, a parallel zone group allocation method is given to allocate different parallel zone groups to data logs with different hotness. After that, a parallel zone group write mechanism is designed to allocate the space of multiple zones in a parallel zone group at the stripe size of a zone, allowing a request to be written to multiple zones in parallel. Extensive experiments based on an NVMe SSD emulator (ConfZNS) show FPZone can effectively improve the utilization of the chip, I/O latency and the performance of F2FS compared to the baseline scheme.