HPC Network Comparison: InfiniBand vs. Ethernet

Date: November 12, 2023

The relentless pursuit of exascale computing and complex AI workloads has pushed high-performance computing (HPC) infrastructure to its limits. At the heart of this evolution lies a critical architectural decision: the choice of interconnect fabric. The debate of InfiniBand vs Ethernet is central to designing efficient HPC networking environments. With NVIDIA's acquisition of Mellanox, a leader in high-performance interconnects, this competition has intensified, driving innovation and compelling data-driven comparisons for enterprise and research clients.

Raw performance is the primary differentiator. InfiniBand, designed explicitly for low-latency, high-throughput data center environments, holds a significant advantage.

• Latency: InfiniBand consistently delivers sub-600 nanosecond end-to-end latency, which is critical for MPI (Message Passing Interface) communication in tightly coupled simulations. Ethernet, even with RoCE (RDMA over Converged Ethernet), typically operates in the microsecond range (>1.2 µs), introducing bottlenecks in parallel workloads.
• Throughput: While both technologies offer 200G and 400G solutions, InfiniBand's congestion control and adaptive routing ensure more consistent and efficient bandwidth utilization, maximizing application performance.

For applications where time-to-solution is paramount, such as climate modeling or genomic sequencing, this performance gap directly translates to research acceleration.

Beyond basic metrics, InfiniBand's architecture introduces paradigm-shifting features that Ethernet struggles to match.

• SHARP (Scalable Hierarchical Aggregation and Reduction Protocol): This groundbreaking feature of Mellanox InfiniBand switches performs arithmetic operations (like MPI reductions) within the network fabric, offloading this task from the CPU. This can accelerate collective operations by up to 50%, a feature unavailable in standard Ethernet.
• Native Congestion Control: InfiniBand's built-in adaptive routing dynamically manages traffic to avoid hotspots. Ethernet relies on additional protocols (e.g., DCQCN) for congestion management, which can be less efficient and require complex tuning.

Ethernet's dominance in general-purpose data centers presents a compelling case based on familiarity and ecosystem.

• Ubiquity and Skillset: Ethernet is universally understood, and a vast pool of network engineers is familiar with its management and troubleshooting. This can reduce operational overhead and training costs.
• Convergence: A single Ethernet fabric can potentially carry storage, data, and management traffic, simplifying network architecture. However, this convergence often requires complex QoS policies to protect performance-sensitive HPC networking traffic.
• Cost: Historically, Ethernet components carried a lower price tag. However, the gap has narrowed significantly with the introduction of high-speed Ethernet and the total cost of ownership (TCO) considering performance-per-watt and performance-per-dollar often favors InfiniBand for dedicated HPC clusters.

The choice between InfiniBand and Ethernet is not a matter of which is universally better, but which is optimal for the specific workload. For pure, mission-critical HPC networking environments—where achieving the fastest time-to-solution for complex calculations is the primary goal—InfiniBand, powered by Mellanox technology, remains the undisputed performance leader. Its advanced in-network computing capabilities and superior efficiency provide a tangible ROI for research and AI-driven enterprises. Conversely, for mixed-workload environments or clusters where extreme performance is less critical, high-speed Ethernet offers a familiar and capable alternative.