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
Temperature State: GREEN
Yellow Threshold : 49 Degree Celsius
Red Threshold : 59 Degree Celsius
SW PID Serial# Status Sys Pwr PoE Pwr Watts
-- ------------------ ---------- --------------- ------- ------- -----
1A NG3K-PWR-715WAC LIT133705FH OK Good Good 715/0
1B C3KX-PWR-715WAC DTN1341K018 Disabled Good Good 715/0
2A Not Present
2B C3KX-PWR-325WAC LIT13330FNM Disabled Good Good 325/0
3A C3KX-PWR-325WAC LIT13330FN3 Disabled Good Good 325/0
3B Not Present
4A C3KX-PWR-350WAC DTN1342L00T OK Good Good 350/0
4B NG3K-PWR-1100WAC LIT13370577 OK Good Good 1100/0
<output truncated>

The output of the show stack-power privileged EXEC command shows the priorities of the powered devices and switches in the power stack.

Switch# show stack-power
Power stack name: Powerstack1
Stack mode: Power sharing

Switch 1:
Power budget: 206
Low port priority value: 17
High port priority value: 16
Switch priority value: 2
Port A status: Not shut
Port B status: Not shut
Neighbor on port A: 0022.bdcf.ab00
Neighbor on port B: 0022.bdd0.4380

Switch 2:
Power budget: 206
Low port priority value: 12
High port priority value: 11
Switch priority value: 1
Port A status: Not shut
Port B status: Not shut
Neighbor on port A: 0022.bdd0.6d00
Neighbor on port B: 0022.bdcf.af80

Switch 3:
Power budget: 656
Low port priority value: 22
High port priority value: 21
Switch priority value: 3
Port A status: Not shut
Port B status: Not shut
Neighbor on port A: 0022.bdcf.af80
Neighbor on port B: 0022.bdd0.6d00

Switch 4:
Power budget: 682
Low port priority value: 27
High port priority value: 26
Switch priority value: 4
Port A status: Not shut
Port B status: Not shut
Neighbor on port A: 0022.bdd0.4380
Neighbor on port B: 0022.bdcf.ab00

If the 715 W or 1100 W power supply fails, devices (powered devices connected to PoE ports and the switches themselves) would be shut down in the this order until power consumption drops below 105% of the rated power of the remaining power supplies:

• Devices connected to Switch 4 low priority ports (priority 27)

• Devices connected to Switch 4 high priority ports (priority 26)

• Devices connected to Switch 3 low priority ports (priority 22)

• Devices connected to Switch 3 high priority ports (priority 21)

• Devices connected to Switch 1 low priority ports (priority 17)

• Devices connected to Switch 1 high priority ports (priority 16)

• Devices connected to Switch 2 low priority ports (priority 12)

• Devices connected to Switch 2 high priority ports (priority 11)

• Switch 4 (priority 4)

• Switch 3 (priority 3)

• Switch 1 (priority 2)

Switch 2 would never have to be shut down because all power would have been lost by the time priority 1 devices were reached.

The output from the show stack-power load-shedding order command shows the order in which devices would shut down in the event of load-shedding:

Switch# show stack-power load-shedding order powerstack-1
Power Stack Stack Stack Total Rsvd Alloc Unused Num Num
Name Mode Topolgy Pwr(W) Pwr(W) Pwr(W) Pwr(W) SW PS
-------------------- ------ ------- ------ ------ ------ ------ --- ---
Powerstack-1 SP-PS Ring 2880 34 473 2373 2 4
Priority Load Switch or PoE
Shed Order Type Devices Shed
---------- ---- ------------------------------------------------------------
22 Lo Gi2/0/16,
21 Lo Gi1/0/13, Gi1/0/20,
12 Hi Gi1/0/7,
4 Sw Switch: 2
3 Sw Switch: 1

This is an example of setting the stack power mode for the stack named power1 to redundant power mode. The largest power supply in the stack is removed from the power budget and used as a backup in case of power supply failure.

Switch(config)# stack-power stack power1  
Switch(config-stackpower)# mode redundant  
Switch(config-stackpower)# exit  

This is an example of setting the switch stack power parameters for switch 3 in the stack that is connected to the power stack with the stack ID power2 . If load-shedding becomes necessary, switches and powered devices in the power stack with the higher numbers are shut down first, with shutdown proceeding in order.

Switch(config)# stack-power switch 3  
Switch(config-switch-stackpower)# stack power2  
Switch(config-switch-stackpower)# power-priority switch 5  
Switch(config-switch-stackpower)# power-priority high 12  
Switch(config-switch-stackpower)# power-priority low 20  
Switch(config-switch-stackpower)# exit  
Switch(config-stackpower)# exit  

Note	Entering the write erase and reload privileged EXEC commands does not change the power priority or power mode non-default configuration saved in the switch flash memory.

This is an example of setting the power priority of a port to high so that it is one of the last ports to shut down in case of a power failure.

Switch(config)# interface gigabitetherent1/0/1  
Switch(config-if)# power inline port priority high  
Switch(config-if)# exit