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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 9 Configuring Catalyst 3750-X StackPower
Understanding StackPower
• System operation can become more green by maximizing power supply efficiency and working with
the most efficient load (30 to 90% of their maximum load).
StackPower uses these terms:
• Available power is the total power available for PoE from all power supplies in the power stack. To
see the available power in a stack, enter the show power inline privileged EXEC command.
• Budgeted power is the power allocated to all powered devices connected to PoE ports in the stack.
Budgeted power is referred to as Used (Watts) in the output of the show power inline command.
• Consumed power is the actual power consumed by the powered devices. Consumed power is
typically less that the budgeted power. To see the consumed power in a stack, enter the show power
inline police privileged EXEC command.
These sections describe stack power:
• StackPower Modes, page 9-2
• Power Priority, page 9-3
• Load Shedding, page 9-3
StackPower Modes
A power stack can run in one of two modes, configured by using the command-line interface:
• In power-sharing mode (the default), all input power is available to be used for power loads. The
total available power in all switches in the power stack (up to four) is treated as a single large power
supply, with power available to all switches and to all powered devices connected to PoE ports. In
this mode, the total available power is used for power budgeting decisions and no power is reserved
to accommodate power-supply failures. If a power supply fails, powered devices and switches could
be shut down (load shedding).
• In redundant mode, the power from the largest power supply in the system is subtracted from the
power budget, which reduces the total available power, but provides backup power in case of a
power-supply failure. Although there is less available power in the pool for switches and powered
devices to draw from, the possibility of having to shut down switches or powered devices in case of
a power failure or extreme power load is reduced.
In addition, you can configure the mode to run a strict power budget or a non-strict (relaxed) power
budget. In both modes, power is denied when there is no more power available in the power budget.
• In strict mode, when a power supply fails and the available power drops below the budgeted power,
the system balances the budget through load shedding of powered devices, even if the actual power
being consumed is less than the available power.
• In non-strict mode, the power stack is allowed to run in an over-allocated state and is stable as long
as the actual power does not exceed the available power. In this mode, a powered device drawing
more than normal power could cause the power stack to start shedding loads. This is normally not a
problem because most devices do not run at full power and the chances of multiple powered devices
in the stack requiring maximum power at the same time is small.
You configure power modes at a power-stack level (that is, the mode is the same for all switches in the
power stack). To configure power-stack parameters, enter the stack-power stack global configuration
command followed by the name of the power stack to enter stack-power configuration mode.