Dell PowerEdge R420 Systems Owner's Manual

Your system supports the Hot Spare feature that significantly reduces the power overhead associated with power supply redundancy.

When the Hot Spare feature is enabled, a redundant power supply is switched to a sleep state. The active power supply supports 100% of the load, thus operating at higher efficiency. The redundant power supply in the sleep state monitors output voltage of the active power supply. If the output voltage of the active power supply drops, the redundant power supply in the sleep state returns to an active output state.

The active power supply can also activate a sleeping power supply if having both power supplies active is more efficient than having the redundant power supply in a sleep state. The power supply defaults are to wake both power supplies if the load on the active power supply is greater than 50% and to sleep the redundant power supply if the load falls below 20%.

You can configure the Hot Spare feature using the iDRAC settings. For more information on iDRAC settings, see the iDRAC7 User's Guide under Software > Systems Management > Dell Remote Access Controllers , at dell.com/support/manuals.