Persimmon: an append-only ZNS-first filesystem

While NAND flash has become the centerpiece of modern data center storage, legacy interfaces impact its performance and lifetime. Emulating in-place updates on SSDs results in frequent garbage collection, causing slowdowns, wear, and write amplification. Changing how we utilize modern SSDs to unlock their full potential is necessary. Even though Zoned Namespace SSDs provide an efficient append-only interface, filesystems on such drives still depend upon in-place updates and fixed metadata addresses, making their use with zoned storage complex and inefficient. We present Persimmon, a fork of the f2fs filesystem built with append-only metadata structures and tuned for zoned names-paces. Persimmon updates f2fs with new in-memory structures for better management in a zoned context, improved checkpoint logic, and append-only metadata management. Persimmon reduces tail latency, background garbage collection, and write amplification. Persimmon adapts its layout to zoned device constraints to unlock greater utilization and better drive cleanup.