Power and 25GbE Port Shortfall in a Six-Node Rack
A customer is installing six VxRail P580N nodes in a single rack. Each node has two 1600 W power supplies; measured idle draw is 420 W and expected peak is 780 W per node. The rack has one 30 A/208 V single-phase PDU; the customer plans to connect both PSUs from each node to that PDU. The ToR switches provide 48x1GbE and 6x25GbE SFP28 ports; the customer ordered 12x25GbE DAC cables for VxRail data ports but no extra switch. Each node also has a dedicated iDRAC port. The rack has 8 free RU and the nodes are 1U. The installer asks whether the power and network design is acceptable and what to do next.
1. Assess the power design. Is one 30 A/208 V PDU acceptable for six nodes?
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Not as designed. Six nodes at 780 W peak is 4,680 W. A 30 A/208 V circuit is 6,240 VA; at a typical 0.9 power factor that is about 5,616 W, and at an 80% derating it is about 4,493 W. The expected peak already exceeds the derated capacity, so the design has little or no headroom and may trip the branch circuit under load. If the power factor is lower, the margin disappears entirely.
The redundancy problem is separate and worse: connecting both PSUs from each node to the same PDU means a PDU or branch-circuit failure takes down every node. VxRail power planning should use two independent PDUs on separate circuits, with each node's PSUs split across them. With one PDU, the customer has no power redundancy even if the wattage fits. Recommendation: add a second PDU/circuit and rebalance PSU cords, or reduce node count/peak load before installation.
2. Assess the network design. Can the ordered cabling and switches support dual-homed 25GbE?
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No. Six nodes with two 25GbE data ports require 12 switch ports for dual-homing. The ToR pair provides only 6x25GbE SFP28 ports total, so at best each node gets one 25GbE link and half the nodes get no 25GbE connection. That is not a redundant VxRail data design. The 48x1GbE ports are fine for iDRAC and out-of-band management, but they are not a substitute for the 25GbE vSAN/vMotion fabric on this model.
Options: add a second 25GbE switch or add enough 25GbE ports to provide two independent switch paths per node; use breakouts only if the switch and VxRail adapter support them and the design is validated; or reduce the cluster to a size the switch can dual-home. Do not deploy with one link per node and call it redundant. Confirm VLAN trunking, MTU 9000 on the 25GbE ports, and that the DACs are supported by both the VxRail network adapter and the switch.
3. What pre-installation checks should be completed before power-on?
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Verify rack readiness first: 8 RU is enough for six 1U nodes, but leave cable-management space and confirm front-to-back airflow matches the rack. Check rail kits, square-hole cage nuts, and that the rack can support the loaded weight. Confirm two independent power circuits and correct PDU types before unpacking.
For each node, record the service tag, iDRAC MAC, and network port labels; confirm iDRAC is cabled to the management switch and has an IP plan. Check that the VxRail software version and firmware baseline are compatible with the ordered model, and that the nodes are not from mixed configurations. Validate 25GbE switch ports, VLAN trunks, MTU, and DAC compatibility. Finally, confirm DNS, NTP, and gateway entries for the VxRail management network; deployment failures at this stage are often planning failures, not hardware faults.