Chapter 3. IBM NeXtScale n1200 Enclosure 53
However, a compute node is restarted only if the FPC determines there is
sufficient power available to power on the server, which is based on the following
factors:
Number of working power supplies
Power policy that is enabled
The oversubscription policy
If there is insufficient power, some compute nodes are not powered on. The
nodes are powered on based on their power usage, lowest first. The objective is
to maximize the number of nodes that can be powered on in a chassis. The
power-on sequence nominally takes about 2 minutes with most of that time spent
by the nodes running a power maximizer. After that is complete, the FPC can
quickly release the nodes to continue to boot.
3.8.2 Power capping
User can choose chassis-level capping or saving or node-level capping or saving
through the power cap configuration options. Power capping allows users to set
a wattage limit on power usage. When it is applied to an individual node, the
node power consumption is capped at an assigned level. When it is applied to a
chassis, the whole chassis power usage is capped. When power saving is
enabled, an individual node or all nodes (chassis level) run in modes of different
throttling level, depending on the modes that are chosen.
3.8.3 Power supply redundancy modes
The FPC offers the following modes from which to choose:
No-redundancy mode
The loss of any power supply can affect the system’s operation or
performance. If the chassis is evaluated to be vulnerable, because of the
failure of one or multiple power supplies, throttle signals are sent to all nodes
in the chassis to be throttled down to the lowest power level possible (CPU or
Memory lowest P-state). In case the power usage remains too high, the
chassis is shut down.
This is the default mode. This mode does not support the oversubscription
mode (see “Power supply oversubscription” on page 54).
N+1 Mode
One installed power supply is used as redundant. The failure of one power
supply is allowed without affecting the system’s operation or performance
(performance can be affected if oversubscription mode is enabled).
This mode can be enabled with oversubscription mode.
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