zns-tools: An eBPF-powered, Cross-Layer Storage Profiling Tool for NVMe ZNS SSDs

Understanding operational characteristics of flash SSDs has been a challenging task due to their complex and closed internals. The recent emergence of Zone Namespace (ZNS) SSDs with their open interface allows the host software stack to explicitly control elements of this complexity, specifically around data placement, grouping, and garbage collection operations. Despite offering more control to applications, due to the opaque and layered nature of the software storage stack, it remains an open challenge to understand, profile, and reason about the data storage and placement decisions on ZNS devices in an end-to-end manner. In this paper, we present zns-tools, an eBPF-powered end-to-end data storage events profiler (https://github.com/stonet- research/znstools) for the whole ZNS-enabled storage stack, including the NVMe/ZNS device driver, Linux block layer, file system, and application. Using zns-tools we uncover diverse utilization profiles of a ZNS device for the same workload (YCSB-A), thus demonstrating the practical utility of zns-tools.