Hot Spare Feature; Removing A Power Supply Unit Blank - Dell EMC PowerEdge R940 Installation And Service Manual

NOTE: When two identical PSUs are installed, power supply redundancy (1+1 – with redundancy or 2+0 – without redundancy) is
configured in system BIOS. In redundant mode, power is supplied to the system equally from both PSUs when Hot Spare is
disabled. When Hot Spare is enabled, one of the PSUs is put into the sleep mode when system utilization is low in order to
maximize efficiency.
NOTE: If two PSUs are used, they must be of the same maximum output power.

Hot spare feature

Your system supports the hot spare feature that significantly reduces the power overhead associated with power supply unit (PSU)
redundancy.
When the hot spare feature is enabled, one of the redundant PSUs is switched to the sleep state. The active PSU supports 100 percent of
the system load, thus operating at higher efficiency. The PSU in the sleep state monitors output voltage of the active PSU. If the output
voltage of the active PSU drops, the PSU in the sleep state returns to an active output state.
If having both PSUs active is more efficient than having one PSU in the sleep state, the active PSU can also activate the sleeping PSU.
The default PSU settings are as follows:
• If the load on the active PSU is more than 50 percent of PSU rated power wattage, then the redundant PSU is switched to the active
state.
• If the load on the active PSU falls below 20 percent of PSU rated power wattage, then the redundant PSU is switched to the sleep
state.
You can configure the hot spare feature by using the iDRAC settings. For more information, see the iDRAC User's Guide available at
Dell.com/idracmanuals.

Removing a power supply unit blank

Prerequisites
Follow the safety guidelines listed in
Steps
If you are installing a second PSU, remove the PSU blank in the bay by pulling the blank outward.
CAUTION: To ensure proper system cooling, the PSU blank must be installed in the second PSU bay in a non-redundant
configuration. Remove the PSU blank only if you are installing a second PSU.
Figure 86. Removing a power supply unit blank
Next steps
Install the PSU blank.
Related links
Installing a power supply unit blank
134 Installing and removing system components
Safety instructions.