Optimization of EXT4 Journaling System Using PLP Requesting Interface on ZNS SSDs

ZNS SSD is a new type of SSD that divides the internal storage space into Zones, which are required to be sequentially written, and allows the host to determine optimal data placement. However, because it doesn’t use a conventional block interface, there are limitations in using the legacy filesystems for ZNS SSD. Specifically, in the case of EXT4 filesystem, unnecessary overhead is generated because the characteristics of journal writing are not considered. In this paper, we propose two techniques to optimize the journaling system of EXT4 filesystem, considering the characteristics of ZNS SSDs. The first technique reduces the write amplification of ZNS SSDs by allocating dedicated zone considering the sequential writing characteristics of the journal. The second technique requests PLP (Persistent Loss Protection) guarantees to the ZNS SSD for the journal, reducing the frequency of internal SSD buffer flushes caused by the journal. The proposed techniques are implemented by modifying the Linux kernel, and performance evaluations are conducted using the FEMU-based emulated ZNS device. Performance evaluations verified that the proposed techniques effectively optimized the EXT4 journaling system for ZNS SSDs, reducing write amplification due to garbage collection and improving I/O performance.