Users Guide

Redundancy Policies
Redundancy policy is a configurable set of properties that determine how CMC manages power to the chassis. The following redundancy
policies are configurable with or without dynamic PSU engagement:
• Grid redundancy
• Power supply redundancy
Grid Redundancy Policy
The purpose of the Grid redundancy policy is to enable a modular enclosure system to operate in a mode in which it can tolerate AC power
failures. These failures may originate in the AC power grid, the cabling and delivery, or a PSU itself.
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.
NOTE: Modify the modular enclosure Redundancy Policy while the enclosure is powered off.
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.
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Managing and Monitoring Power