A technician is preparing a 42-U four-post cabinet that will be installed in a raised-floor data-center row that uses a hot-aisle/cold-aisle arrangement. The rack must hold two 4-U, 95 kg rack-mount UPS units, sixteen 2-U servers that move air front-to-back, and one 1-U network switch. Which rack layout BEST follows industry guidelines for cooling efficiency and safety?
Mount the UPS units in the center of the rack to balance weight, alternate server orientation every 2 U, and place the switch at the top rear of the cabinet.
Put the UPS units at the top rear of the rack, install the switch at the bottom front, and mount all servers below the UPS with their exhaust facing the cold aisle.
Install both UPS units in the lowest 8 U, mount every server so its intake faces the cold aisle directly above the UPS, and place the switch in the top-front U positions.
Start with servers in the lowest positions, mount the UPS units directly above them, and install the switch halfway up the rack to shorten Ethernet runs.
Best practice is to keep the rack's center of gravity low by mounting the heaviest devices-such as battery-based UPS modules-in the lowest available U positions. All equipment that cools front-to-back should have its intake facing the cold aisle so that hot exhaust is discharged only into the hot aisle. Lightweight devices such as top-of-rack switches can safely be placed at the upper front of the cabinet. The layout that places the UPS units in the bottom 8 U, all servers above them with their fronts toward the cold aisle, and the switch in the highest front position therefore meets both cooling and tip-over safety recommendations. The other options either put heavy equipment high in the rack, reverse server airflow into the cold aisle, or alternate orientations in ways that recirculate hot air and complicate cable management.
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Why is it important to place heavy equipment like UPS units in the lowest U positions of a rack?
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Why should the intake of front-to-back cooling servers always face the cold aisle?