Integrated Dell Remote Access Controller 7 (iDRAC7) Version 1.50.50 User's Guide

You can configure the power supply options such as redundancy policy, hot spare, and power factor correction.

Hot spare is a power supply feature that configures redundant Power Supply Units (PSUs) to turn off depending on the server load. This allows the remaining PSUs to operate at a higher load and efficiency. This requires PSUs that support this feature, so that it quickly powers ON when needed.

In a two PSU system, either PSU1 or PSU2 can be configured as the primary PSU. In a four PSU system, you must set the pair of PSUs (1+1 or 2+2) as the primary PSU.

After Hot Spare is enabled, PSUs can become active or go to sleep based on load. If Hot Spare is enabled, asymmetric electrical current sharing between the two PSUs is enabled. One PSU is awake and provides the majority of the current; the other PSU is in sleep mode and provides a small amount of the current. This is often called 1 + 0 with two PSUs and hot spare enabled. If all PSU-1s are on Circuit-A and all PSU-2s are on Circuit-B, then with hot spare enabled (default hot spare factory configuration), Circuit-B has much less load and triggers the warnings. If hot spare is disabled, the electrical current sharing is 50-50 between the two PSUs, the Circuit-A and Circuit-B normally has the same load.

Power factor is the ratio of real power consumed to the apparent power. When power factor correction is enabled, the server consumes a small amount of power when the host is OFF. By default, power factor correction is enabled when the server is shipped from the factory.