Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual page 1283

Copyright © 2010, Juniper Networks, Inc.
If the switch starts receiving insufficient power because of power supply failure or some
other problem, power management powers off the line cards in reverse-priority order
until power (including redundant power) is sufficient for the remaining cards. Thus
higher priority line cards are more likely to retain power in power shortage conditions
than are lower priority line cards.
Power management responds to changes in power availability and line card operating
status by powering line cards on or off as appropriate. For example, if you add a power
supply, lower priority cards that were powered off due to insufficient power are powered
on in priority order.
If you take a line card offline, power management no longer allocates power to it. If
power to the switch is insufficient when you take a line card offline, power management
allocates the freed power to a lower priority card that was offline due to lack of power
and brings it online. Restarting a line card, however, does not affect the power allocated
to it. Thus when power is insufficient, restarting a line card does not change its operating
status or the operating status of other line cards.
NOTE: Because power management does not allocate power to an offline
line card, a line card that has been taken offline in an EX8200 switch is not
automatically brought online when you commit a configuration. You must
explicitly bring the line card online with the
slot-number online
running Junos operating system (Junos OS), which automatically bring an
offline FPC online when you commit a configuration.
The actual power priority of a slot is determined first by the slot's assigned priority and
second by the slot's number. If more than one slot has the same assigned priority, power
priority is determined by slot number, with the lowest-numbered slots receiving power
first.
By default, all slots are assigned the lowest priority. You can assign a priority to a slot
using the CLI. If you do not explicitly assign priorities to slots, the slots receive power in
ascending order of slot numbers.
Because the purpose of power management is to ensure minimal system disruption
when power is insufficient, slot power priority does not always determine which line cards
receive power. In some cases, power management might provide power to a lower priority
line card rather than a higher priority line card. For example:
If power is insufficient for a line card in a higher priority slot but is sufficient for a line
card in a lower priority slot, the lower priority slot receives the power. For example, if
an 8-port SFP+ line card requiring 450 W is in a higher priority slot than a 48-port SFP
line card requiring 330 W, the 48-port SFP line card receives the power if there is more
than 330 W but less than 450 W available.
In an operating switch that has insufficient power, power management does not power
off operating line cards to provide power to a newly inserted line card or a line card
that is brought online after being offline, even if the line card has a higher priority than
the currently operating line cards.
Chapter 50: High Availability—Overview
request chassis fpc slot
command. This behavior differs from other platforms
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