An MQM9700-NS2F and an MQM9700-NS2R provide the same advertised switching capability, but move air in opposite directions. Substituting one for the other changes how the switch must be positioned relative to the rack’s cold and hot aisles.
A second substitution—from QM9700 to QM9790—changes the management architecture.
For operators buying existing inventory, these differences determine whether a switch can replace an installed unit, join a planned deployment or serve as a usable spare.
Read the complete ordering code
NVIDIA distinguishes four configurations:
• MQM9700-NS2F — Managed. Air enters at the power-supply side and exits at the connector side.
• MQM9700-NS2R — Managed. Air enters at the connector side and exits at the power-supply side.
• MQM9790-NS2F — Unmanaged. Air enters at the power-supply side and exits at the connector side.
• MQM9790-NS2R — Unmanaged. Air enters at the connector side and exits at the power-supply side.
All four are listed as Quantum-2 systems with 64 NDR ports through 32 OSFP ports. Matching port counts and speeds do not make them interchangeable. Source: NVIDIA ordering information.
An RFQ stating only “QM9700, 400G” leaves the airflow requirement unresolved. A quotation stating “QM9700 or equivalent” can leave both airflow and management open to interpretation.
Specify airflow against the installed orientation
Consider a rack where the switch’s connector side faces the hot aisle to simplify connections to server NICs.
In that arrangement, a power-to-connector unit draws air from the cold aisle and exhausts toward the hot aisle. Installing a connector-to-power unit in the same orientation reverses that path: its intake faces the hot aisle.
If the connector side instead faces the cold aisle, the required airflow direction reverses.
That is why “front-to-back” is an inadequate purchasing description unless both parties define the front. Specify power-to-connector or connector-to-power, together with the intended connector-side orientation.
NVIDIA instructs planners to align equipment airflow within the rack. Its installation guidance identifies power-to-connector units with blue airflow indicators and connector-to-power units with red indicators on the power side. Source: NVIDIA installation guidance.
Rotating the chassis may change its relationship to the aisles, but also changes cable routing and service access. Evaluate those consequences against the rack design before accepting an alternative.
Verify the installed fans and power supplies
The chassis label should not be the only evidence used to qualify a refurbished switch.
NVIDIA specifies that fan-module airflow must match every installed power supply. It also requires fans to match the system’s intended airflow. Opposing directions affect internal temperature and heat dissipation. Source: NVIDIA FRU replacement guidance.
For a surplus lot, request photographs of the chassis identification label and the installed fan and PSU labels. Check these against the manufacturer’s supported configuration.
A replacement component may fit mechanically without satisfying the thermal requirement. Equally, a switch that powers on successfully has not demonstrated acceptable operation under sustained load.
If a supplier proposes converting airflow, request confirmation of the supported conversion procedure and the complete replacement-component list. Do not assume that replacing fans alone establishes a valid configuration.
QM9790 changes the management plan
NVIDIA’s managed systems include an embedded management CPU running MLNX-OS. The documented management environment provides interfaces such as CLI, WebUI and SNMP.
The QM9790 is listed as unmanaged. This does not remove the InfiniBand fabric’s requirement for a Subnet Manager: NVIDIA specifies that one must run on a suitable switch or a connected host.
Its documentation also describes a different firmware-maintenance path for externally managed switches, normally using in-band access and NVIDIA’s firmware tools. Source: NVIDIA software management documentation.
For an operator already using external fabric management, a QM9790 may fit the architecture. For a deployment expecting the replacement switch to provide onboard management, it is a design change.
Before approving the substitution, establish where the Subnet Manager runs, how the switch will be monitored and how firmware maintenance will be performed. The purchasing decision should preserve those operating requirements.
Define acceptance before the lot ships
For these systems, we recommend recording five acceptance items against each serial number.
1. Equipment identity
Confirm the complete ordering code against equipment-label photographs. Record any differences between units rather than treating the entire lot as one uniform configuration.
2. Thermal configuration
Verify installed fan and PSU part numbers, consistent airflow and compatibility with the intended rack orientation.
3. Management
Confirm the required management access and successful discovery within the intended fabric. Establish the firmware baseline and the maintenance method that operations will use.
4. Link validation
Check negotiated speeds and error counters using the proposed cables or optics. Record which ports were tested and under what conditions.
5. Completeness
List installed components, mounting hardware and included accessories explicitly. Identify anything the buyer must source separately before installation.
A sample test can qualify the proposed configuration, but it does not establish that every unit in a mixed lot has identical components. Sellers should identify exceptions before shipment.
For spares procurement, this is particularly important. A spare only reduces recovery time if it can replace the failed unit within the existing rack and management design.
Make surplus networking inventory easier to evaluate
For sellers, complete part numbers and component photographs reduce ambiguity before technical review. A lot described simply as “Quantum-2 400G switches” leaves buyers to determine which units fit their installation.
Separating inventory by model, airflow direction, installed components and condition makes it easier to match equipment to a specific requirement. It also helps buyers distinguish a direct replacement from an alternative that requires additional work.
REVO.tech helps buyers evaluate networking offers against deployment requirements and helps sellers present surplus equipment clearly.
Send your required switch part number, airflow direction, management needs, quantity and delivery destination to [email protected].
For surplus switches, include complete part numbers and clear chassis, fan and PSU label photographs.
Technical reference article. NVIDIA documentation checked November 5, 2026.