Mitigating Write Buffer Thrashing in Zoned UFS with a Dedicated fsync Stream

Recently, a novel Zoned Namespace (ZNS) storage device called Zoned UFS was proposed to integrate the zoned storage interface into mobile flash storage systems. Unlike typical server-oriented ZNS SSDs, Zoned UFS supports only a limited number of write buffers due to its constrained SRAM size. Consequently, when multiple open zones are simultaneously utilized by users or the file system, write buffers must be frequently switched among zones, causing buffer thrashing. This buffer thrashing triggers additional SLC writes and reads, introducing significant overhead. In this paper, we propose employing a dedicated data stream specifically for synchronous writes to minimize write buffer thrashing. Furthermore, we leverage existing hot/cold data separation techniques by increasing the number of data streams within F2FS, effectively maintaining low segment cleaning costs. Experimental evaluations demonstrate that our approach reduces buffer thrashing occurrences by up to 70% and achieves a 7–14% reduction in fsync tail latency.