Users Guide

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.
● In a Power Supply Redundancy configuration, 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 configuration, a minimum of two PSUs are always turned
on.
Because an enclosure in the Power Supply Redundancy configuration 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 configuration, all PSUs are engaged when the chassis is turned on. Power utilization is monitored,
and if system configuration 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 configuration cause the engagement of PSUs from the Standby
state. This maintains the mirrored configuration needed for dual-grid redundancy.
NOTE:
With DPSE in enabled state, if power demand increases in both the two Power Redundancy policy modes, the
standby PSUs are brought Online to reclaim power.
Default Redundancy Configuration
As shown in the table here, the default redundancy configuration for a chassis depends on the number of PSUs that it contains.
Table 36. Default Redundancy Configuration
PSU Configuration Default Redundancy Policy Default Dynamic PSU Engagement Setting
Two PSUs DC Redundancy Disabled
Four PSUs DC Redundancy Disabled
Grid Redundancy
In Grid redundancy mode with four PSUs, all four PSUs are active. The two PSUs must connect to one AC power grid, while the
other two PSUs are connect to the other AC power grid.
CAUTION:
To avoid a system failure, and for Grid redundancy to work effectively, there must be a balanced set
of PSUs properly cabled to separate AC grids.
If one AC grid fails, the PSUs on the functioning AC grid take over, without interrupting the servers or infrastructure.
CAUTION:
In Grid redundancy mode, you must have balanced sets of PSUs (at least one PSU in each grid). If
this condition is not met, Grid redundancy is not possible.
Managing and Monitoring Power 163