Users Guide

Power Supply Redundancy Policy
The power supply redundancy policy is useful when redundant power grids are not available, but you may want to be protected against a
single PSU failure bringing down your servers in a modular enclosure. The highest capacity PSU is kept in online reserve for this purpose.
This forms a Power Supply redundancy pool.
PSUs beyond those required for power and redundancy are still available and is added to the pool in the event of a failure.
Unlike Grid redundancy, when power supply redundancy is selected, CMC does not require the PSU units to be present in any specic PSU
slot positions.
NOTE: Dynamic Power Supply Engagement (DPSE) allows PSUs to be placed in standby. The standby state indicates a physical
state of PSUs that are not supplying power. When you enable DPSE, the extra PSUs may be placed in Standby mode to increase
eciency and save power.
NOTE: Modify the modular enclosure Redundancy Policy while the enclosure is powered o.
Dynamic Power Supply Engagement
By default, Dynamic Power Supply Engagement (DPSE) mode is disabled. DPSE saves power by optimizing the power eciency of the
PSUs that supply power to the chassis. This also results in increased PSU life, and reduced heat generation. To use this feature, you must
have an Enterprise License.
CMC monitors total enclosure power allocation, and moves the PSUs into Standby state, causing the total power allocation of the chassis
to be delivered through fewer PSUs. As the online PSUs are more ecient when running at higher utilization, it improves their eciency
and longevity of the standby PSUs.
To operate remaining PSUs at their maximum eciency, use the following power redundancy modes:
• PSU Redundancy mode with DPSE provides power eciency. At least two supplies are online, with one PSU required to power the
conguration, and one to provide redundancy in case of a PSU failure. PSU Redundancy mode oers protection against the failure of
any one PSU, but oers no protection in the event of an AC grid loss.
• Grid Redundancy mode with DPSE, where at least two PSUs are active, one on each power grid. Grid redundancy also balances the
eciency and maximum availability for a partially-loaded modular enclosure conguration.
• Disabling DPSE provides the lowest eciency as all four supplies are active and share the load, resulting in lower utilization of each
power supply.
DPSE can be enabled for all two power supply redundancy congurations explained above — Power Supply Redundancy, and Grid
Redundancy.
NOTE
: In a two PSU conguration modes, server load may prevent any PSU from changing to the Standby mode.
• In a Power Supply Redundancy conguration, in addition to the PSUs required to power the enclosure, the enclosure always keeps an
additional PSU powered on and marked Online. Power utilization is monitored and one PSU can be moved to Standby state on the
basis of overall system load. In a four PSU conguration, a minimum of two PSUs are always turned on.
Because an enclosure in the Power Supply Redundancy conguration always has an extra PSU engaged, the enclosure can
accommodate the loss of one online PSU and still have enough power for the installed server modules. The loss of the online PSU
causes a standby PSU to come online. Simultaneous failure of multiple PSUs may result in the loss of power to some server modules
while the standby PSUs are turning on.
• In Grid Redundancy conguration, all PSUs are engaged when the chassis is turned on. Power utilization is monitored, and if system
conguration and power utilization allows, PSUs are moved to the Standby state. Because the Online status of PSUs in a grid mirrors
that of the other grid, the enclosure can sustain the loss of power to an entire grid with no interruption of power to the enclosure.
An increase in power demand in the Grid Redundancy conguration cause the engagement of PSUs from the Standby state. This
maintains the mirrored conguration needed for dual-grid redundancy.
Managing and Monitoring Power
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