Power Supply Redundancy Policy; Dynamic Power Supply Engagement - Dell EMC PowerEdge VRTX User Manual

When you configure a system for Grid redundancy, the PSUs are divided into grids: PSUs in slots 1 and 2 are in the first grid while
PSUs in slots 3 and 4 are in the second grid. CMC manages power so that if there is a failure of either grid, the system continues to
operate without any degradation. Grid redundancy also tolerates failures of individual PSUs.
NOTE: One role of Grid redundancy is to provide seamless server operation despite failure of a whole power grid, but the
most power is available to maintain Grid redundancy when the capacities of the two grids are approximately equal.
NOTE: Grid redundancy is only met when the load requirements do not exceed the capacity of the weakest power grid.
Grid Redundancy Levels
One PSU in each grid is the minimum configuration necessary for use as grid redundant. Additional configurations are possible with
every combination that has at least one PSU in each grid. However, to make the maximum power available for use, the total power
of the PSUs in each leg should be as close to equal as practical. The upper limit of power while maintaining Grid redundancy is the
power available on the weakest of the two grids.
If a CMC is unable to maintain Grid redundancy, an e-mail and/or SNMP alert is sent to administrators, if the Redundancy Lost event
is configured for alerting.
In the event of a single PSU not functioning in this configuration, the remaining PSUs in the problematic grid are marked as online. In
this state, the PSUs in the Redundant Grid if not in failed state, help in functioning of the system without interruption. If a PSU stops
functioning, the chassis health is marked non-critical. If the smaller grid cannot support the total chassis power allocations, then Grid
redundancy status is reported as No, and the health of chassis is displayed as Critical.

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
specific 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 efficiency and save power.

Dynamic Power Supply Engagement

By default, Dynamic Power Supply Engagement (DPSE) mode is disabled. DPSE saves power by optimizing the power efficiency 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 efficient when running at higher utilization, it improves
their efficiency and longevity of the standby PSUs.
To operate remaining PSUs at their maximum efficiency, use the following power redundancy modes:
• PSU Redundancy mode with DPSE provides power efficiency. At least two supplies are online, with one PSU required to power
the configuration, and one to provide redundancy in case of a PSU failure. PSU Redundancy mode offers protection against the
failure of any one PSU, but offers 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 efficiency and maximum availability for a partially-loaded modular enclosure configuration.
• Disabling DPSE provides the lowest efficiency 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 configurations explained above — Power Supply Redundancy, and Grid
Redundancy.
NOTE: In a two PSU configuration modes, server load may prevent any PSU from changing to the Standby mode.
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