Quick Comparison Table
| Feature | ConnectX-5 | ConnectX-6 |
|---|---|---|
| Max Speed | 100Gb/s | 200Gb/s (HDR) / 100GbE (HDR100) |
| PCIe Interface | PCIe 3.0/4.0 x16 | PCIe 4.0 x16 |
| GPUDirect | GPUDirect RDMA | GPUDirect RDMA + Storage |
When to Choose ConnectX-5
ConnectX-5 is the better value choice when your workload does not need 200GbE/HDR speeds. Used ConnectX-5 adapters cost 40-60% less than equivalent ConnectX-6 models.
When to Choose ConnectX-6
ConnectX-6 adds GPUDirect Storage and hardware-accelerated TLS/IPsec encryption. Required for HDR InfiniBand fabrics and AI/ML training clusters.
The Verdict
ConnectX-5 delivers approximately 95% of ConnectX-6 performance at 40-60% lower cost. Choose ConnectX-5 for budget deployments, ConnectX-6 for AI/ML and security.
Browse ConnectX adapters at zhongxindata.hk
Which ConnectX generation fits your server slots
- PCIe 3.0 x16 servers can run ConnectX-5 at full 100Gb/s; ConnectX-6 needs PCIe 4.0 x16 for its 200Gb/s paths
- Check the physical slot width before buying — a x8 slot halves the usable bandwidth of either card
- Server-generation note: ConnectX-6 is the natural fit for Xeon 6 / Sapphire Rapids-era platforms
Cabling and connector differences that matter in the rack
- ConnectX-5 ships as QSFP28 (100GbE) or QSFP56 (200GbE) depending on the SKU; ConnectX-6 uses QSFP56 for 200GbE
- Transceiver choice differs: 100GbE optics work on ConnectX-5 but you need 200G-capable optics for ConnectX-6 at full rate
- Mixed-speed fabrics are common — plan for the adapter that matches your switch ports, not just the CPU
How we test used Mellanox adapters before listing them
- Every unit is cleaned, re-flashed and bench-tested on our own test line before it is listed
- We confirm port speed, negotiated link rate, firmware level and error counters against the part number you send
- Ask us for photos of the actual unit and the firmware level before you commit
Related reading
- MCX516A-CCAT 100GbE adapter — the ConnectX-5 side of the comparison, with real stock behind it
- MCX653105A-ECAT 100GbE adapter — the ConnectX-6 side, PCIe 4.0 x16
- ConnectX-7 vs ConnectX-8 — next generation for readers planning beyond ConnectX-6
- Network adapters — category hub for all Mellanox NICs
Frequently Asked Questions
Is ConnectX-6 worth the upgrade over ConnectX-5?
It depends on where the bottleneck is. If your server has PCIe 3.0 slots or your fabric is 100GbE, ConnectX-5 already saturates the link and ConnectX-6 adds cost without extra throughput. ConnectX-6 earns its place when you move to 200GbE links, run PCIe 4.0 x16, or need a newer adapter in a server where firmware support for the older card has ended.
Can a ConnectX-6 card run in a PCIe 3.0 slot?
Yes. The card is backward compatible and will link at the PCIe 3.0 rate the slot provides. At PCIe 3.0 x16 the usable host bandwidth is around 15.75 GB/s, which is above what 100GbE consumes but below what 200GbE needs. In practice you get full 100GbE with some headroom, not full 200GbE.
Which ConnectX-5 SKU should I buy for a 100GbE switch?
For QSFP28 100GbE on PCIe 3.0 x16, the MCX516A-CCAT is the common choice. If your server has a PCIe 4.0 x16 slot and you want a newer generation, look at the MCX653105A-ECAT. The -CCAT and -CDAT suffixes describe the medium and speed grade, so match the suffix to your cabling plan rather than the marketing name.
Do ConnectX-5 and ConnectX-6 cards share the same cabling?
They can share optics at 100GbE. ConnectX-6 adds 200GbE over QSFP56, and that needs 200G-capable transceivers or cabling. In a mixed fabric you can run 100G optics on both card families, so a staged upgrade does not force you to replace cabling in the same step.
How do you confirm a used Mellanox adapter actually works?
We clean, re-flash and bench-test on our own test line, then confirm the part number, port speed, negotiated link rate and firmware level. We check error counters as well, so a card that reports link but produces errors does not get listed. You can ask for photos of the exact unit and its firmware level before you commit.
Will a used ConnectX adapter accept current firmware?
In most cases yes, but it depends on the card and the image. Some older adapters need the intermediate release before the newest one. We re-flash during testing and report the firmware level we ship, so you know the starting point rather than finding out at install time.