HDR100 is 100Gb/s InfiniBand that runs on two of an HDR port's four 50G lanes. Its purpose is port count: a 40-port QM8700 or QM8790 HDR switch can split every port with a 200G-to-2×100G splitter cable and serve up to 80 HDR100 adapters. The adapter on each split leg is a ConnectX-6 such as the MCX653105A-ECAT, and the cable is the MCP7H50 family. That costs less per node than giving every server a full 200G port, and in PCIe 3.0 servers it's all the bandwidth the slot can carry anyway.
Below: how HDR100 differs from EDR, the switch setup, the parts list and when the full 200G card is worth it.
Short answer: one HDR port, two HDR100 nodes
HDR100 adapters and splitters, from $80 at Resilient Tec
Two ECAT nodes share one split switch port, so you need half the switch ports per node.
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MCX653105A-ECAT — ConnectX-6 VPI, 1 × HDR100 / 100GbE The adapter for a split leg. PCIe 3.0/4.0 x16. |
$389.95 · Refurbished, in stock at Resilient Tec |
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MCP7H50-H001R30 — 200G QSFP56 to 2 × HDR100 splitter, 1 m One switch port to two adapters. |
$80 · New, in stock at Resilient Tec |
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MCP7H50-H002R26 — 200G QSFP56 to 2 × HDR100 splitter, 2 m For servers further down the rack. |
$92 · New, in stock at Resilient Tec |
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MCX653105A-HDAT — ConnectX-6 VPI, 1 × HDR 200G For nodes that get a full, unsplit port. |
$619.95 · Refurbished, in stock at Resilient Tec |
Resilient Tec sells the MCX653105A-ECAT for $389.95, the MCP7H50-H001R30 for $80 and the MCX653105A-HDAT for $619.95 directly at resilient-tec.com. Adapters are refurbished genuine NVIDIA; splitters are new compatible. Lifetime warranty, shipping from Knoxville, Tennessee. Prices checked October 22, 2026. POs and net terms available.
HDR100 vs EDR vs HDR
- EDR (ConnectX-5): 100Gb/s on four 25G NRZ lanes, QSFP28.
- HDR100 (ConnectX-6 ECAT): 100Gb/s on two 50G PAM4 lanes, QSFP56.
- HDR (ConnectX-6 HDAT): 200Gb/s on four 50G PAM4 lanes, QSFP56.
The lane count is why splitting works: a four-lane HDR port divides cleanly into two two-lane HDR100 ports. EDR and HDR100 are both "100G," but a split leg is a two-lane HDR100 link. Put ConnectX-6 HDR100 adapters on split legs and EDR ConnectX-5 cards on full ports.
Switch Setup on a QM8700 / QM8790
- Enable the split-ready system profile. Per NVIDIA's QM87xx manual, the switch must run its split-ready profile before any port can split. In this profile the switch reports 81 logical ports, one of which is an internal SHARP port.
- Split the port to two HDR100 ports with the module-type split setting in MLNX-OS. The exact syntax is in the InfiniBand Switching chapter of the MLNX-OS user manual for your release.
- Expect the port config to reset. NVIDIA's manual states that splitting an interface deletes all configuration on that interface.
- Cable it. The 200G end of the splitter goes into the switch and the two 100G ends go into the adapters.
Every QSFP56 port on the QM8700 can be split, and NVIDIA lists no blocking rules for neighboring ports. Ethernet switches are different: see port splitting on the SN2100 and SN2700.
When the Full 200G Card Is Worth It
- Yes: PCIe 4.0 servers doing heavy all-reduce or storage traffic on a full HDR port. Use the MCX653105A-HDAT (refurbished, $619.95).
- No: PCIe 3.0 servers such as the R740xd and R640, which top out near 100 Gb/s in any case (why), and nodes on a split port.
Moving part of an HDR fabric to NDR? The MFA7U10-H003 bridges NDR and HDR, and 200G HDR optics are covered in our MMA1T00-HS guide.
FAQ
What is HDR100?
100Gb/s InfiniBand that uses HDR signalling on two lanes. An HDR port has four 50Gb/s PAM4 lanes; HDR100 uses two of them. That lets one 200G HDR switch port feed two 100G adapters through a splitter cable.
Is HDR100 the same as EDR?
No. Both run at 100Gb/s, but EDR uses four 25Gb/s NRZ lanes and HDR100 uses two 50Gb/s PAM4 lanes. A split HDR100 leg is a two-lane connection, so plan on HDR100-capable ConnectX-6 adapters such as the MCX653105A-ECAT on split ports, and put EDR adapters on full, unsplit ports.
How many HDR100 ports does a QM8700 support?
The QM8700 has 40 QSFP56 ports, and NVIDIA's manual says all of them can be split in two. In the split-ready profile the switch reports 81 logical ports, one of which is an internal SHARP port, so up to 80 HDR100 ports.
What cable splits an HDR port into two HDR100 ports?
A 200G QSFP56 to 2 × 100G QSFP56 splitter, NVIDIA part family MCP7H50. Resilient Tec sells the MCP7H50-H001R30 (new, $80) and the MCP7H50-H002R26 (new, $92).
Should I buy MCX653105A-ECAT or MCX653105A-HDAT?
ECAT if the node will sit on a split HDR100 port or in a PCIe 3.0 server, where 200G can't be used anyway. HDAT if it gets a full HDR port in a PCIe 4.0 server. At Resilient Tec: MCX653105A-ECAT (refurbished, $389.95), MCX653105A-HDAT (refurbished, $619.95).
Does splitting a QM8700 port erase its configuration?
Yes. NVIDIA's manual states that splitting an interface deletes all configuration on that interface, and the switch has to be in its split-ready system profile first. Plan the change for a maintenance window.
Ready to Buy?
The HDR100 parts list. Lifetime warranty, shipping from Knoxville, Tennessee. Prices below checked October 22, 2026.
- MCX653105A-ECAT — ConnectX-6 VPI, 1 × HDR100 / 100GbE — $389.95, refurbished, in stock at Resilient Tec; genuine NVIDIA, the split-leg adapter
- MCP7H50-H001R30 — HDR 200G to 2 × HDR100 splitter DAC, 1 m — $80, new, in stock at Resilient Tec; NVIDIA/Mellanox-coded compatible
- MCP7H50-H002R26 — HDR 200G to 2 × HDR100 splitter DAC, 2 m — $92, new, in stock at Resilient Tec; NVIDIA/Mellanox-coded compatible
- MCX653105A-HDAT — ConnectX-6 VPI, 1 × HDR 200G — $619.95, refurbished, in stock at Resilient Tec; for full ports in PCIe 4.0 servers
- MMA1T00-HS — 200G QSFP56 HDR SR4 transceiver — $239, new, in stock at Resilient Tec; for HDR runs past copper reach
Sizing an HDR fabric? Send us your node count and switch model for a complete parts list.
You Might Also Need
- Why a 200G ConnectX-6 tops out near 100G — PCIe Gen3 explained
- How to read a ConnectX part number — every MCX suffix decoded
- MFA7U10-H003 — bridging NDR and HDR
- Is a third-party MMA1T00-HS safe? — 200G HDR optics
- InfiniBand vs Ethernet for AI clusters — which fabric fits your stack