Introduction
As AI workloads, NVMe-oF storage fabrics, and high-density virtualization push network demands beyond 10GbE, 100GbE datacenter switches have become the new baseline for modern infrastructure. Mellanox Spectrum switches are among the most widely deployed 100GbE platforms in the world — and for good reason.
This guide introduces the Mellanox Spectrum switch family, explains key specifications, and helps you choose the right model for your environment.
Why 100GbE?
10GbE was the datacenter standard for over a decade, but modern workloads have outgrown it:
- NVMe SSDs can saturate a 10GbE link in milliseconds
- GPU-to-GPU communication in AI clusters requires ultra-low latency and high bandwidth
- Storage replication and backup windows shrink dramatically at 100GbE
- A single 100GbE uplink replaces four 25GbE links, simplifying cabling
Mellanox Spectrum Switch Family Overview
SN2700 — 32-Port 100GbE
The SN2700 is the most widely deployed Mellanox Spectrum switch. It offers 32 ports of 100GbE QSFP28 in a 1U form factor, with a total switching capacity of 6.4 Tbps.
- Ports: 32x 100GbE QSFP28
- Throughput: 6.4 Tbps / 4.76 Bpps
- Latency: Cut-through under 300ns
- Best for: Top-of-rack (ToR) switching, spine-leaf fabrics, NVMe-oF
SN3700 — 36-Port 100GbE High Density
The SN3700 uses the Spectrum-2 ASIC and delivers 36 ports of 100GbE with enhanced RoCE v2 and in-network computing capabilities.
- Ports: 36x 100GbE QSFP28
- Throughput: 7.2 Tbps
- Features: SHARP in-network aggregation, enhanced RoCE v2
- Best for: AI/ML clusters, HPC spine switches
SN3800 — 64-Port 100GbE
The SN3800 is a 2U high-density switch with 64 ports of 100GbE, ideal for large spine layers or aggregation switching.
- Ports: 64x 100GbE QSFP28
- Throughput: 12.8 Tbps
- Best for: Spine aggregation, large-scale storage clusters
Key Features of Mellanox Spectrum Switches
- Onyx OS: Mellanox’s native NOS with full CLI, REST API, and Ansible support
- Open Ethernet: Supports Cumulus Linux, SONiC, and other open NOS options
- RoCE v2: Hardware-accelerated RDMA over Ethernet for NVMe-oF and AI workloads
- Cut-through switching: Sub-300ns latency for latency-sensitive applications
- ECMP: Equal-cost multipath routing for spine-leaf load balancing
Spine-Leaf Architecture with Mellanox Spectrum
The most common deployment pattern for Mellanox Spectrum switches is a spine-leaf fabric:
- Leaf switches (SN2700): Connect servers via 25GbE or 100GbE uplinks
- Spine switches (SN3700/SN3800): Interconnect all leaf switches with 100GbE uplinks
- This architecture provides predictable latency, easy scaling, and full bisectional bandwidth
Buy Used Mellanox Spectrum Switches
Zhongxin Data stocks used Mellanox SN2700, SN3700, SN3800, and SN4600 switches. All units are fully tested, firmware-verified, and shipped with warranty from Hong Kong, China.
Contact us for bulk pricing or configuration assistance.
The Spectrum family mapped to deployment tiers
- SN2100 is the edge and aggregation tier where 100GbE is enough
- SN3700 is the mainstream 200GbE workhorse, and the default for a modern pod
- SN3800 and SN4600 add 400GbE headroom for spine tiers and AI fabrics that need it
Comparing the specs that decide the fit
- Port count, port speed and breakout support together determine how many servers a switch attaches
- Buffer depth decides whether the switch absorbs a burst or passes congestion upstream
- Form factor constrains rack density: a 64-port 2U unit occupies twice the height of a 1U
Software, airflow and the operational commitment
- Decide between an ONIE unit and a unit with a network OS installed before you order
- Airflow direction is fixed by the chassis — match it to your hot-aisle or cold-aisle layout
- On a used switch, ask for the firmware level and the fan configuration, since both affect behaviour
Related reading
- SN2700 100GbE switch — the entry-tier Spectrum unit
- Switch evolution 100G to 800G — generation context
- Spectrum selection guide — the deeper selection article
- Network switches — category hub
Frequently Asked Questions
Which Mellanox Spectrum switch should I buy for 100GbE?
For most data center pods, the SN3700 is the default answer — dense 100GbE or 200GbE ports in 1U with a mature software stack. The SN2100 covers edge and aggregation where 100GbE is more than you need. If your spine tier is the constraint, look at the SN3800 or SN4600 for the extra headroom. Tell us the server count and the port speed you need and we will size it with you.
What is the difference between the SN3700 and SN3800?
The SN3800 moves to 400GbE and typically comes in a 2U chassis with more ports and deeper buffers, while the SN3700 is a 1U 200GbE platform. Choose the SN3800 where the spine tier needs 400G headroom; the SN3700 is the better value where it is already dense enough.
Is Spectrum-4 the same as Spectrum-3?
No. Spectrum-4 is the newer generation, and the SN5600 is its flagship 800GbE switch built for AI fabrics. Spectrum-3 covers the SN3800 and SN4600 generation. A Spectrum-3 switch remains a solid choice where 200GbE or 400GbE is the right ceiling; Spectrum-4 is for fabrics that need 800G links.
Do I need to buy the network OS separately?
It depends on the unit. An ONIE build ships without a network OS so you can install the one you standardise on, while a unit with an OS installed is ready to configure. On a used switch we state exactly which of the two you are receiving, along with the firmware level.
How do you verify a used Spectrum switch?
We clean, re-flash and bench-test on our own test line, then confirm the port count, port speed, airflow direction, fan configuration and firmware level against the part number. Ask for photos of the actual unit and the firmware level before you commit.
Can a 100GbE switch take a 25GbE server?
Yes, where the switch supports breakout on the port. A 100GbE switch with QSFP28 cages can present 25GbE on compatible ports and a 25GbE adapter will negotiate down. That is the usual staged migration path and it lets you adopt 100GbE uplinks without 25GbE access switches.