Cisco Catalyst 3560-X Series, Software Configuration Manual

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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring Catalyst 3750-X StackPower
Understanding Cisco StackPower
Load Shedding
Load shedding is the process of shutting down devices in case of power supply, cable, or system failures.
In general, Cisco StackPower supports only single faults; for example, a single power supply failing, a
single cable breaking, or a single system halting operation.
For power stacks in power-sharing mode, there are two types of load-shedding: immediate and graceful.
• Immediate load shed occurs when a failure could cause the power stack to fail very quickly. For
example, if the largest power supply in the power stack fails, this could cause the stack to
immediately start shutting down powered devices.
•
Graceful load-shedding can occur when a smaller power supply fails. Switches and powered devices
are shut down in order of their configured priority, starting with devices with priority 27, until the
power budget matches the input power.
Graceful load shedding is always enabled and immediate load shedding occurs only when necessary, so
both can occur at the same time.
Note Load shedding does not occur in redundant mode unless two or more power supplies fail, because the
largest power supply is used as a backup power source.
Notes on load shedding:
•
The method (immediate or graceful) is not user-configurable, but is based on the power budget.
• Immediate load shedding also occurs in the order of configured priority, but occurs very quickly to
prevent hardware damage caused by loss of power.
•
If a switch is shut down because of load shedding, the output of the show stack-power privileged
EXEC command still includes the MAC address of the shut down switch as a neighbor switch, even
though the switch is down. This command output shows the StackPower topology, even if there is
not enough power to power up a switch.
Immediate Load Shedding Example
For power stacks in power-sharing mode, if a large power supply in the power stack fails, the stack
immediately starts shutting down powered devices until the power budget matches the input power. Cisco
StackPower can support multiple power supply failures if the total amount of power lost is less than or
equal to one-half the total input power. For example, in a power stack with four 1100 W power supplies,
the power stack can lose two 1100 W power supplies and continue to operate. In addition, Cisco
StackPower can support a loss of more than one-half of the total input power when the power supply
failures are more than five minutes apart.
This example has a power stack of four switches ( Powerstack1 ) in power sharing mode and shows which
devices would be shut down in the immediate load shedding process caused by loss of either of two
power supplies.
The output of the show env all command shows that power supplies included in power sharing are a
715 W power supply in switch 1, and one 350 W and one 1100 W power supply in switch 4. Other power
supplies are inactive (disabled or not present).
Switch# show env all
FAN 1 is OK
FAN 2 is OK
FAN PS-1 is OK
FAN PS-2 is OK
TEMPERATURE is OK
Temperature Value: 30 Degree Celsius