116 IBM NeXtScale System Planning and Implementation Guide
5.1 Power planning
In this section, we provide example best practices for configuring power
connections and power distribution to meet electrical safety standards while
providing a wanted level of redundancy, and cooling for racks that contain
NeXtScale System chassis and servers.
For more information, see IBM NeXtScale System Power Requirements Guide,
PRS4401, which is available at this website:
http://ibm.com/support/techdocs/atsmastr.nsf/WebIndex/PRS4401
NeXtScale System offers N+1 and N+N power supply redundancy policies at the
chassis level. To minimize system cost, it is expected that N+1 or non-redundant
power configurations are used; therefore, this is how the power system was
optimized.
When you are planning your power sources for a NeXtScale System rack
configuration, remember the following important considerations:
Input voltage
Power supply input is single phase 100 - 120 Volt alternating current (VAC) or
200 - 240 VAC. For NeXtScale System servers in production environments,
200 - 240 VAC is preferred because it reduces the electrical current
requirement. Another consideration is that the power supplies produce less
DC output at the lower range.
Power distribution unit (PDU) input: single-phase or three-phase power
PDUs can be fed with single-phase or three-phase power. Three-phase
power provides more usable power to each PDU and to the equipment. The
IBM three-phase PDUs separate the phases, which provide single-phase
power to the power supplies. The NeXtScale n1200 Enclosure’s six power
supplies were designed to evenly balance the load on three-phase power
systems.
Single or dual power feed (N+N) to the rack
With a dual-power feed, half of the rack PDUs are powered by one feed and
the other half is powered by the second feed, which provides redundant
power to the rack.
N+N designs can provide resilience if a power feed must be powered down for
maintenance, or in the event of power disruption. However, careful power
planning must be done to assure there is adequate power for the NeXtScale
systems to keep running on only one power feed.
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