Torrent: Re-Architecting End-to-End Transmission for Cross-Datacenter RDMA Networks

Sustainability is becoming increasingly challenging in today's data centers with limited space, power and connectivity. Large cloud service providers interconnect geographically distributed datacenters for better scalability and availability. Applications running on cross-datacenter network impose great challenges in transport design. In this paper, we identify two inherent limitations of extending the existing transport technology, RDMA, and its Ethernet derivative, RoCE, to long-haul transmission. First, the on-chip resources of commodity RDMA NICs are insufficient for long-haul transmission. Second, applying existing traffic control schemes to inter-datacenter environment exhibits poor performance. Motivated by this, we propose Torrent, a switch-driven transport framework which partitions end-to-end control into three sub-control loops. To achieve the combined goals of fairness and high performance in cross-datacenter scenarios, Torrent employs fast acknowledgment and near-end congestion control on datacenter interconnection (DCI) switches. We implement Torrent prototypes on commodity programmable switches and evaluate it through real-world testbed experiments. Our results show that Torrent can achieve high link utilization over ultra-long distances and quickly converge congested flows to steady rates.