User's Manual

218 Power Management
NOTICE: In AC Redundancy mode, a difference in the number of PSUs between the
two AC grids (for example, three PSUs on one AC grid and two on the other AC grid)
will cause a degradation in the redundancy.
Power Supply Redundancy
The capacity of a PSU in the chassis is kept as a spare, ensuring that a failure
of any one PSU will not cause the servers or chassis to power-down. Power
Supply Redundancy mode requires four PSUs to operate correctly; any
additional PSUs will not be utilized. Failure of two PSUs may cause the
servers in the chassis to power down.
No Redundancy
Power from up to three PSUs is used to power on the entire chassis.
NOTICE: The No Redundancy mode uses only three PSUs without a backup.
Failure of one of the three PSUs being used could cause servers to lose power and
data.
Power Conservation and Power Budget Changes
The CMC performs power conservation when the user-configured maximum
power limit is reached. When the demand for power exceeds the power limit
you have set, the CMC reduces power to servers you assign a lower priority to
free power for higher priority servers and other modules in the chassis.
If all or multiple slots in the chassis are configured with the same priority
level, the CMC decreases power to servers by increasing slot number order.
For example, if the servers in slots 1 and 2 have the same priority level, the
power for the server in slot 1 is decreased before that of the server in slot 2.
NOTE: You can assign a priority level to each of the servers in the chassis by giving
each server a number from 1 through 9 inclusive. The default priority level for all
servers is 1. The lower the number, the higher the priority level. For instructions on
assigning server priority levels, see "Using RACADM" on page 237.
PSU Failure With a No Redundancy Policy
The CMC decreases power to servers when an insufficient power event
occurs, such as a PSU failure. After decreasing power on servers, the CMC re-
evaluates the power needs of the chassis. Power for higher priority servers is
restored incrementally while power needs remain within the power budget.