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Emerging Zoned Namespace (ZNS) SSDs, providing the coarse-grained zone abstraction, hold the potential to significantly enhance the cost efficiency of future storage infrastructure and mitigate performance unpredictability. However, existing ZNS SSDs have a static zoned interface, making them in-adaptable to workload runtime behavior, unscalable to underlying hardware capabilities, and interfering with co-located zones. Applications either under-provision the zone resources yielding unsatisfied throughput, create over-provisioned zones and incur costs, or experience unexpected I/O latencies. We propose eZNS, an elastic-ZNS interface that exposes an adaptive zone with predictable characteristics. eZNS comprises two major components: a zone arbiter that manages zone allocation and active resources on the control plane, and a hierarchical I/O scheduler with read congestion control and write admission control on the data plane. Together, eZNS enables the transparent use of a ZNS SSD and closes the gap between application requirements and zone interface properties. Our evaluations over RocksDB demonstrate that eZNS outperforms a static zoned interface by 17.7% and 80.3% in throughput and tail latency, respectively, at most. 

Routable PCIe has become the predominant cluster interconnect to build emerging composable infrastructures. Empowered by PCIe non-transparent bridge devices, PCIe transactions can traverse multiple switching domains, enabling a server to elastically integrate a number of remote PCIe devices as local ones. However, it is unclear how to move data or perform communication efficiently over the routable PCIe fabric without understanding its capabilities and limitations. This paper presents the design and implementation of rPCIeBench, a software-hardware co-designed benchmarking framework to systematically characterize the routable PCIe fabric. rPCIeBench provides flexible data communication primitives, exposes end-to-end PCIe transaction observability, and enables reconfigurable experiment deployment. Using rPCIeBench, we first analyze the communication characteristics of a routable PCIe path, quantify its performance tax, and compare it with the local PCIe link. We then use it to dissect in-fabric traffic orchestration behaviors and draw three interesting findings: approximate max-min bandwidth partition, fast end-to-end bandwidth synchronization, and interference-free among orthogonal data paths. Finally, we encode gathered characterization insights as traffic orchestration rules and develop an edge constraints relaxing algorithm to estimate PCIe flow transmission performance over a shared fabric. We validate its accuracy and demonstrate its potential to provide an optimization guide to design efficient flow schedulers.