Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual page 1285

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NOTE: To achieve the reduction in reserved chassis power, power
management reduces the maximum fan speed to 60 percent in an N+N
configuration from 80 percent in an N+1 configuration. Because the maximum
fan speed is reduced, it is possible that a line card that overheats would be
shut down sooner in an N+N configuration than in an N+1 configuration.
Power management automatically recalculates the redundant power and normal
operating power as power supplies go online or offline. For example, if you have an N+N
configuration with three online 2000 W power supplies, power management allocates
2000 W to redundant power. If you bring a fourth 2000 W power supply online, power
management then allocates 4000 W to redundant power. If a power supply goes offline
again, power management once again allocates 2000 W to redundant power.
When power is insufficient to meet the budgeted power requirements, power management
raises alarms as follows:
If all the line cards are receiving power but insufficient redundant power exists to
maintain the configured N+1 or N+N power configuration, power management raises
a minor (yellow) alarm. If this condition persists for 5 minutes, the alarm becomes a
major (red) alarm.
If one or more line cards are down because of insufficient power (including redundant
power), power management raises a major (red) alarm.
Power management clears all alarms when sufficient power is available to meet normal
operating and redundant power requirements.
Understanding Alarm Types and Severity Levels on EX Series Switches on page 629
Configuring the Power Priority of Line Cards (CLI Procedure) on page 1195
Configuring Power Supply Redundancy (CLI Procedure) on page 1194
Verifying Power Configuration and Use on page 1204
Chapter 50: High Availability—Overview
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