Choosing the Right NVIDIA Mellanox Network Switch
NVIDIA Mellanox network switches form the backbone of modern high-performance data center fabrics. Whether building an AI training cluster, a storage network, or a general-purpose fabric, selecting the correct switch model directly impacts bandwidth, latency, and cost efficiency. This guide compares SN3700, SN3800, and SN2100.
Switch Specifications Comparison
| Specification | SN3700 | SN3800 | SN2100 |
|---|---|---|---|
| Chipset | Spectrum-3 | Spectrum-4 | Spectrum-2 |
| Max Port Speed | HDR 200Gb/s | NDR 400Gb/s | EDR 100Gb/s |
| Total Ports | 64 x HDR200 | 8 x NDR400 + 16 x HDR200 | 16 x EDR100 |
| Aggregate Throughput | 12.8 Tbps | 51.2 Tbps | 1.6 Tbps |
| Packet Buffer | 64 MB shared | 128 MB shared | 16 MB shared |
| Latency | ~130 ns | ~100 ns | ~190 ns |
| Power | 350W | 550W | 75W |
| RoCEv2 | Yes | Yes | Yes |
| Protocol | Ethernet (RoCEv2) | Ethernet (RoCEv2) | Ethernet (RoCEv2) |
| Ethernet Mode | Yes | Yes | Yes |
SN3700: The Versatile 200Gb/s Workhorse
The SN3700 is the most widely deployed Mellanox switch. Its 64 HDR 200Gb/s ports make it ideal for AI training leaf/spine, storage fabrics, HPC interconnect, and general data center L2/L3 switching. Key advantage: runs RoCEv2 (RDMA over Converged Ethernet), which gives InfiniBand-style RDMA on an Ethernet fabric; native InfiniBand needs a Quantum switch such as the QM8700.
SN3800: The 400Gb/s Next-Generation Core
The SN3800 (Spectrum-4) is designed for H100/H200 GPU infrastructure: 8 NDR 400Gb/s ports + 16 HDR 200Gb/s ports, 51.2 Tbps throughput. Key advantage: Gradual HDR-to-NDR migration without replacing the entire fabric.
SN2100: The Entry-Level 100Gb/s Edge
The SN2100 is the cost-effective choice: 16 x 100Gb/s ports, 75W power. Ideal for small AI clusters (8-16 GPUs), edge/top-of-rack, and budget-constrained projects.
Decision Matrix
| Scenario | Recommended Switch | Reason |
|---|---|---|
| AI cluster 256-1024 GPUs | SN3700 + SN3800 | HDR/NDR bisection |
| AI cluster 32-128 GPUs | SN3700 | Full HDR, cost-effective |
| AI cluster 8-16 GPUs | SN2100 | Low cost, adequate 100Gb/s |
| Storage fabric (all-flash) | SN3700 | 200Gb/s NVMe-oF |
| HPC simulation | SN3700 (RoCEv2) | Sub-us latency |
Reading the switch spec table correctly
- Port count in a spec table is cage count, not usable link count — check the 1:1 or 2:1 breakout ratio
- Airflow direction is a physical property, not a preference: P2C and C2P units are not interchangeable in the same rack row
- Form factor constrains the deployment: 1U for a rack row, 2U when you need more ports or deeper buffers
Choosing between the SN3700, SN3800 and SN2100
- SN3700 is the 200GbE workhorse for mainstream fabrics with a mature software stack
- SN3800 moves to 400GbE for fabrics where the spine tier needs the headroom
- SN2100 is the entry point for smaller 100GbE builds and edge aggregation
Software and licensing questions to settle before you buy
- Confirm whether the unit ships as ONIE or with a network OS already licensed, and what you are actually paying for
- The network OS choice is a real operational commitment — it decides how you configure and monitor the box
- On a used unit, ask for the firmware level and the license state, not just the model name
Related reading
- SN3700 100GbE switch — the SN3700 side of the comparison
- SN3800 100GbE switch — the SN3800 side
- Data center switch evolution — where the portfolio is heading
- Network switches — category hub
Frequently Asked Questions
What is the difference between SN3700 and SN3800?
The SN3700 is a 200GbE platform and the SN3800 moves to 400GbE, typically in a 2U chassis with more ports and deeper buffers. Choose the SN3800 when your spine tier needs the 400G headroom; the SN3700 remains the value pick for mainstream 200G fabrics where it is already dense enough.
Is the SN2100 still worth buying for a new build?
Yes, for 100GbE aggregation and smaller builds it remains a sensible entry point with a mature feature set. For a new AI training fabric you would normally look at 200GbE or above, but for edge aggregation, storage networking and homelab-class 100GbE the SN2100 still does the job.
Does the switch model determine which optics I need?
The port cage type and speed rating do. QSFP28 cages serve 100GbE and QSFP56 cages serve 200GbE, so a 200GbE switch cannot be populated with 100G optics without a breakout path. We will confirm the cage type and the optic options for the exact part number before you quote.
What does P2C versus C2P airflow mean in practice?
P2C means the fan draws air from the front and pushes it toward the connector, matching a cold-aisle front-to-back layout. C2P is the mirror image for hot-aisle rows. The two are physically different chassis, so an airflow direction is fixed at purchase and cannot be changed by configuration.
Should I buy a switch with a network OS already installed?
It depends on your team. A unit with the OS already licensed is ready to configure, while an ONIE unit lets you install the OS you standardise on. Both are legitimate; the point is to know which you are getting. On a used unit we state the firmware level and what is installed.
How do you verify a used Mellanox switch before shipping it?
We clean, re-flash and bench-test on our own test line, then confirm port count, port speed, airflow direction and firmware level against the part number. We also report the fan configuration. Ask for photos of the actual unit before you commit.