Selecting a Power distribution unit PDU for a 9508

[MichaelAngelica1906]

ooking for a Power distribution Unit PDU to support a Cisco 9508 that has 8 power supplies,

I attached the hardware reference guide. The wattage used is dependent on the supervisor and line cards in the switch. Initially we have 2 Supervisor B+ (N9K-SUP-B+) modules at 80W each and 2 36-port 100-Gigabit Ethernet QSFP28 line card (N9K-X9736C-FX) at 720W each. That’s 1600W. We anticipate fully

populating the switch with the 100-Gig line cards. So that’s 8 X 720W, plus the SUP-B+ cards = 5920W. Given that, we only need 2 3000W Power supplies. However, this is an always ON application, so I want it to be with n+2 redundancy on generator and non-generator. That’s why I have 8 Power supply per switch.

So the power supply total from one power feed from 2 switches would be 24000W. I’m not sure how that works. If 8 power supplies come on at the same time, do they all try to pull 3000W of power? Do we account for that, or do we account for the fully populated max of 5920W?

[Jason Leschnik]

The power supplies should only ever draw the load required by the hardware. For instance an PC with a 1000 watt PSU will not be constantly drawing 1000 watt if it's only loaded with 250 watt (peak) of hardware [e.g. a Motherboard + CPU say 100 + 150 watt each]. The power supplies will share the load of all the attached equipment at 1/8th. Here are the outputs from my lab switch. 

As you can see here, by default it's splitting the load over both Power supplies.

Leaf-7# show en
encryption    environment   
Leaf-7# show environment power 
Power Supply:
Voltage: 12 Volts
Power                      Actual             Actual        Total
Supply    Model            Output             Input      Capacity       Status
                           (Watts )           (Watts )     (Watts )
-------  ----------  ---------------  ------  ----------  --------------------
1        N9K-PAC-3000W-B       731 W              749 W      3000 W      Ok
2        N9K-PAC-3000W-B       654 W              696 W      3000 W      Ok
3        N9K-PAC-3000W-B         0 W                0 W         0 W   Shutdown
4        ------------            0 W                0 W         0 W   Absent


                                  Actual        Power      
Module    Model                     Draw    Allocated    Status
                                 (Watts )     (Watts )     
-------  -------------------  -----------  -----------  --------------
1        N9K-X9564PX             228.00 W     399.60 W    Powered-Up
2        N9K-X9636PQ             183.00 W     399.60 W    Powered-Up
3        N9K-X9536PQ             239.00 W     399.60 W    Powered-Up
4        N9K-X9464PX              94.00 W     240.00 W    Powered-Up
Xb21     N9K-C9504-FM             72.00 W     130.80 W    Powered-Up
Xb22     N9K-C9504-FM             75.00 W     130.80 W    Powered-Up
Xb23     N9K-C9504-FM             77.00 W     130.80 W    Powered-Up
Xb24     N9K-C9504-FM             82.00 W     130.80 W    Powered-Up
Xb25     N9K-C9504-FM             76.00 W     130.80 W    Powered-Up
Xb26     N9K-C9504-FM             83.00 W     130.80 W    Powered-Up
27       N9K-SUP-B                78.00 W      90.00 W    Powered-Up
28       N9K-SUP-B                74.00 W      90.00 W    Powered-Up
29       N9K-SC-A                 14.00 W      25.20 W    Powered-Up
30       N9K-SC-A                 14.00 W      25.20 W    Powered-Up
fan1     N9K-C9504-FAN            31.00 W     129.00 W    Powered-Up
fan2     N9K-C9504-FAN            30.00 W     129.00 W    Powered-Up
fan3     N9K-C9504-FAN            31.00 W     129.00 W    Powered-Up

N/A - Per module power not available


Power Usage Summary:
--------------------
Power Supply redundancy mode (configured)                PS-Redundant
Power Supply redundancy mode (operational)               PS-Redundant

Total Power Capacity (based on configured mode)            3000.00 W
Total Grid-A (first half of PS slots) Power Capacity       6000.00 W
Total Grid-B (second half of PS slots) Power Capacity         0.00 W
Total Power of all Inputs (cumulative)                     6000.00 W
Total Power Output (actual draw)                           1386.00 W
Total Power Input (actual draw)                            1446.00 W
Total Power Allocated (budget)                             2843.00 W
Total Power Available for additional modules                157.00 W

HTH

Regards,

Jason.