A GPU cluster is a networking project with accelerators attached. Here is how to think about front-end and back-end fabrics, and where small clusters most often lose their performance.
What to check
- Separate the fabrics conceptually from the start: a front-end network for users, storage and management, and a back-end network dedicated to accelerator-to-accelerator traffic.
- Decide whether you actually need a dedicated back-end fabric. Single-node and small multi-node inference often does not, and the money is better spent elsewhere.
- Match NIC count and placement to GPU topology. A NIC on the wrong CPU socket or sharing a PCIe root with several GPUs will cap throughput regardless of switch capacity.
- If you are using RDMA over Ethernet, plan the congestion control and lossless configuration as part of the design, not as post-installation tuning.
- Size storage traffic explicitly. Checkpoint writes and data loading can saturate a front-end network that was sized only for user traffic.
- Design the management and out-of-band network properly. Recovering a wedged node remotely is worth far more than it costs.
- Leave port and optics headroom for one more node group. Cabling and optics changes are the disruptive part of expansion, not the servers.
- Confirm optics and cable compatibility against the specific switch and NIC part numbers, including breakout configurations.
The ETON view
Almost every underperforming small GPU cluster we are asked to look at has a networking or topology cause rather than a compute one. The accelerators were chosen carefully, the fabric was chosen last, and the two do not match. It is a predictable outcome of buying compute and network from different conversations.
The reference architectures published by the large vendors are genuinely useful here, and we recommend reading them as design patterns: separate front-end and back-end fabrics, a properly specified out-of-band network, and NIC placement that matches the GPU topology. What we would not do is assume you must buy the whole bundled architecture to get those properties. Below roughly a rack, you can implement the same design with standard switching and adapters at a very different price, and lead times you can actually plan around.
Design the topology first, then let us source the switching, adapters and optics against it. Vendor neutral, on availability and lead time, with the part numbers checked before you order.
Related infrastructure
Category: Networking · Vendor: ETON Technology · Technology: Ethernet fabrics, InfiniBand, RDMA, spine-and-leaf, NICs · Last verified: 02 Sep 2026 · ~2 min read
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