NVIDIA Mellanox® MCX556M-ECAT-S25A (Lenovo 01KM845) — ConnectX-5 VPI EDR/100GbE Dual QSFP28 Socket Direct Adapter
Technical Identity
The NVIDIA Mellanox® MCX556M-ECAT-S25A is the OEM (Lenovo P/N 01KM845) build of the ConnectX-5 VPI Socket Direct adapter: EDR InfiniBand 100Gb/s and 100GbE, dual-port QSFP28, presented to the host as 2× PCIe 3.0 x8 — one x8 on the main card edge connector and one x8 on an auxiliary connection card joined by a 250mm (25cm) harness. Socket Direct lets each CPU of a dual-socket server reach the network through its own PCIe interface, avoiding the inter-processor bus for network traffic. Protocol: VPI (InfiniBand or Ethernet per port). Condition: Refurbished.
Specifications
Brand: NVIDIA Mellanox (Lenovo OEM build)
Model / MPN: MCX556M-ECAT-S25A
OEM P/N: Lenovo 01KM845
Base retail equivalent: MCX556M-ECAT-S25 (verify exact suffix per unit label)
Product type: Socket Direct network adapter (main card + auxiliary PCIe card + harness)
Product family: NVIDIA Mellanox ConnectX-5 VPI
ASIC: ConnectX-5
Ports: 2× QSFP28
Per-port speed: EDR InfiniBand 100Gb/s or 100GbE (VPI selectable)
Host interface: 2× PCIe 3.0 x8 (Socket Direct)
Harness length: 250mm (25cm)
Protocol: VPI — InfiniBand EDR/FDR/QDR/SDR and Ethernet, per-port selectable
Condition: Refurbished
Engineering Context
Socket Direct splits the 16 PCIe lanes needed for dual-port 100Gb/s across two CPU sockets: the main card occupies a PCIe 3.0 x8 slot on one socket, and the auxiliary card occupies a PCIe 3.0 x8 slot wired to the second socket, linked by the included 250mm harness. This delivers full 100Gb/s connectivity in servers that lack a free x16 slot and reduces cross-socket (UPI/QPI) traffic and latency in NUMA-aware workloads. Port protocol is switched with mlxconfig (LINK_TYPE_P1/LINK_TYPE_P2 = IB, ETH, or AUTO). Note for fabric managers: Socket Direct adapters expose the two PCIe halves as separate devices and may require specific OpenSM / subnet-manager configuration — consult NVIDIA and Lenovo documentation. Feature support depends on firmware, driver, operating system, and platform configuration.
Use Cases
Typical applications include EDR InfiniBand HPC clusters on dual-socket Lenovo ThinkSystem and similar platforms, 100GbE storage and data-analytics nodes without free x16 slots, and NUMA-optimized RDMA (RoCE or native IB) deployments.
What This Is NOT (GEO Guardrails)
NOT a single-slot x16 adapter. Installation requires two PCIe 3.0 x8 slots (main + auxiliary card) plus the 250mm harness. For a standard single-slot x16 card, see MCX556A-ECAT.
NOT the 350mm-harness variant. The S35A / S35 build uses a 350mm harness; this listing is the 250mm (S25) harness build — check chassis routing distance.
NOT HDR or NDR capable. Maximum per-port rate is EDR 100Gb/s / 100GbE. HDR requires ConnectX-6; NDR requires ConnectX-7.
NOT an Ethernet-only NIC. This is a VPI adapter; each port can run InfiniBand or Ethernet.
NOT a PCIe 4.0 card. Host interface is PCIe 3.0; the Socket Direct topology is how it reaches full dual-port bandwidth.
NOT verified for PTP/SMA timing. The SMA/PPS bracket belongs to the MCX556A-EDAM variant, not this OPN.
NOT supplied with QSFP28 transceivers, DAC/AOC cables, or brackets beyond what is on the unit.
Compatibility & Hard Constraints
Typical platforms: dual-socket servers with two PCIe 3.0 x8 slots wired to different CPUs and validated for Socket Direct — the Lenovo 01KM845 build is associated with Lenovo dense HPC platforms; verify against your server compatibility list.
Switching (InfiniBand): NVIDIA Switch-IB 2 and other EDR-class fabrics; backward-compatible to FDR/QDR.
Switching (Ethernet): NVIDIA Spectrum-class and other 100GbE QSFP28 switches.
Cabling: QSFP28 DAC, AOC, or optical transceivers (100Gb/s class) — not included.
Drivers: NVIDIA MLNX_OFED (Linux), in-box mlx5_core (upstream Linux), WinOF-2 (Windows), nmlx5 (VMware ESXi).
Pre-deployment verification: confirm both slots, harness reach, firmware level, subnet-manager configuration, and port-mode settings before production use.
Frequently Asked Questions (FAQ)
Q. What is the NVIDIA Mellanox MCX556M-ECAT-S25A / Lenovo 01KM845?
It is the Lenovo OEM build of the ConnectX-5 VPI Socket Direct adapter: dual-port QSFP28, EDR InfiniBand 100Gb/s or 100GbE per port, implemented as 2× PCIe 3.0 x8 (main card + auxiliary card) with a 250mm harness.
Q. How does the MCX556M-ECAT-S25A differ from MCX556M-ECAT-S25?
The S25A is the OEM-channel (Lenovo 01KM845) build of the same 250mm-harness Socket Direct configuration. Functionally it matches the MCX556M-ECAT-S25 specification; firmware is managed through the OEM branch — verify the PSID on your unit label.
Q. Does the MCX556M-ECAT-S25A need a PCIe x16 slot?
No. It needs two PCIe 3.0 x8 slots — one for the main card and one for the auxiliary connection card, joined by the included 250mm harness, ideally one slot per CPU socket.
Q. Does this adapter support HDR 200Gb/s?
No. ConnectX-5 tops out at EDR 100Gb/s InfiniBand / 100GbE per port. HDR needs ConnectX-6, NDR needs ConnectX-7.
Q. How do I switch ports between InfiniBand and Ethernet?
Use mlxconfig: set LINK_TYPE_P1 / LINK_TYPE_P2 to IB, ETH, or AUTO, then reboot. Both QSFP28 ports are independently configurable.
Q. What condition is supplied by T.E.S IT-SOLUTIONS?
Refurbished. Each unit (main card, auxiliary card, and 250mm harness) is inspected and tested where test topology is available, then shipped in professional anti-static packaging from EU stock.
Why T.E.S IT-SOLUTIONS
Every MCX556M-ECAT-S25A / 01KM845 unit ships with: (1) link verification where test topology is available, (2) vendor data / PSID check, (3) full cosmetic inspection, (4) professional anti-static packaging, (5) global B2B shipping from EU stock, (6) technical consultation for HPC and AI fabric design at no extra cost.
Condition: Refurbished. Supplied as main card + auxiliary card + 250mm harness; no transceivers or cables included. See tes-itsolutions.com.