Network Hardware, Racks, and Power/Cooling
Physical hardware questions cover racks and cabinets, RU sizing, rail and mounting standards, airflow direction, and cable management within the enclosure. Know the difference between two-post and four-post racks, cabinet depth, and why front-to-back airflow must match switch port orientation. Understand power distribution: circuits, PDUs, redundancy with A and B feeds, UPS sizing, and load balancing. Cooling topics include hot and cold aisles, blanking panels, and avoiding recirculation.
Candidates should be able to estimate power and heat: watts convert to British thermal units per hour, and UPS runtime depends on load. Redundancy requires independent sources, not two cords on one strip. Also know environmental limits and monitoring.
Traps: assuming dual power supplies provide redundancy when both connect to the same circuit; ignoring airflow direction when mounting switches; leaving empty rack units open and causing hot air recirculation; and undersizing cooling by counting only nameplate watts.
Rule of thumb: keep utilization below about 80 percent of circuit and UPS capacity, and verify that each redundant feed traces to a separate source.
Worked example: a rack draws 3,000 W. Convert to about 10,240 BTU per hour (3,000 times 3.41). Confirm cooling capacity exceeds that figure with margin, and confirm each PDU feed is on a separate circuit.
Key concepts
- Rack types and RU planning
- Airflow and hot/cold aisles
- Power redundancy and UPS sizing
- Heat load estimation