HP BL40p Optimizing facility operation in high density data center environment - Page 11
Liquid cooled racks, a server reboot to occur without errors. - blade servers
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In addition, any gaps between the cold and hot isles allow hot exhaust air to re-circulate and mix with cold air, making a "short circuit". This situation can occur when hot aisle exhaust air flows straight through a rack with open "U" spaces as shown in Figure 5. Gaskets or blanking panels must be installed in any open spaces in the front of the rack to support the front-to-back airflow design and prevent these negative effects. All rack space must be filled by equipment or enclosed by blanking panels so that the cool air is routed exclusively through the equipment and cannot bypass through or around the rack. Figure 5. Airflow in rack without blanking panels (top) and with blanking panels (bottom) Heat loads generated by blade servers in given rack configurations can be calculated by using the HP BladeSystem Power Sizer found at: www.hp.com/go/bladesystem/powercalculator. Proper cable management practices: • Segregate power and data cables. Cables in close proximity to each other, especially those oriented in parallel or in loops, can create electromagnetic interference (EMI) through induction. • Use cable routing and retention products. Cable rings, trays, and trunking products will reduce problems associated with cooling, EMI, and cable damage. • Employ new cable trays to allow routing of cables above the racks rather than in plenum sub flooring, remove obstructions to airflow in the data center. • Use CAT5 KVM cabling. The smaller, more flexible form factor of CAT5 cabling facilitates routing through the rack and its customizable lengths eliminate coils of cabling in the rear of the rack. The Interface Adapter (IA) that connects from the CAT5 cable to the server KVM port also provides keep-alive and naming functionality. Keep-alive means that even if the CAT5 cable is disconnected from the switch the IA will still respond as if the keyboard, mouse and video were present, allowing a server reboot to occur without errors. Liquid cooled racks The rack itself is not the limiting factor in high density rack configurations. Instead, the maximum heat load for air cooled racks is determined by the air volume and the air temperature being delivered to the rack. The average maximum load for air cooled racks is about 10kW/rack. The actual maximum load is dependant on the optimization of variables like data center design, placement of high density racks, the use of closely coupled cooling techniques, and the other best practices addressed in this document. When some or all of these techniques are optimized in concert, the actual load can go beyond 10 kW/rack. Liquid-cooled racks embody the concept of "closely coupled" cooling where the cooling mechanism is in close proximity to the servers to be cooled and is aware of the specific 11