Power Supply Redundancy - Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual

Complete Software Guide for Junos

Power Supply Redundancy

1180
®
OS for EX Series Ethernet Switches, Release 10.4
However, if you restart the switch, power management reruns the current power budget
policy and powers line cards on or off based on their priority. As a result, line cards
receive power strictly by priority order and previously operating line cards might no
longer receive power.
If you change the assigned power priority of line cards when there is insufficient power
for all the line cards, power management does not power down line cards that had
been receiving power because they are now a lower priority.
By default, power management in EX8200 switches is configured to manage the power
supplies for N+1 redundancy, in which one power supply is held in reserve for backup if
one of the other power supplies is removed or fails.
You can configure power management to manage the power supplies for N+N
redundancy. In N+N redundancy, power management holds N power supplies in reserve
for backup. For example, if your switch has six power supplies and you configure N+N
redundancy, power management makes three power supplies available for normal
operating power and reserves three power supplies for redundancy (3+3). If you have an
odd number of power supplies, power management allocates one more power supply
to normal operating power than to redundant power. For example, if you have five power
supplies, the N+N configuration is 3+2.
Given the same number of power supplies, an N+N configuration usually provides less
normal operating power than an N+1 configuration because the N+N configuration holds
more power in reserve for backup. Table 178 on page 1180 shows the effect on normal
operating power in N+1 and N+N configurations.
Table 178: Available Operating Power in N+1 and N+N Redundancy
Configurations
Number of Power Normal Operating Power in N+1
Supplies at n W Each Configuration
2 1 x (n W)
3 2 x (n W)
4 3 x (n W)
5 4 x (n W)
6 5 x (n W)
To compensate for the reduced normal operating power, power management reserves
less power to the chassis in an N+N configuration than in an N+1 configuration. This
reduction in reserved chassis power allows a switch in an N+N configuration to power
more line cards than it could without the reduction. For the EX8208 switch, the power
reserved for the chassis is reduced to 1200 W from 1600 W; for the EX8216 switch, it is
reduced to 1800 W from 2400 W.
Normal Operating Power in
N+N Configuration
1 x (n W)
2 x (n W)
2 x (n W)
3 x (n W)
3 x (n W)
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