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Fed Beginner
Beginner

3850 Stack-power questions

Hi everyone,

 

While investigating a load shed problem (%PLATFORM_STACKPOWER-4-ILS_EVENT) which affected a few of our 3850 stacks configured in "Power sharing strict" mode, we came across a few concepts for which we haven't found any clear documentation yet. While we understand cause (power outage to all PSU's in slots A) and outcome (load shedding) of this issue, the following are still unclear:

 

- How does a Power Stack calculate the Reserved power? We have seen different values for stacks with the same topology/mode/Total Power.

- How is Total Allocated Power (Total less Rsvd) distributed between members of the same Power Stack if no specific configuration is present? "sh stack-power budgeting"provided values which we tried to correlate to actual Consumed power (Sys/PoE) or even to device classes and CDP with no success.

- Is power budgeting per member calculated differently if a Power Stack is configured for Power Sharing non-strict vs strict mode?

- How fast do budgeting calculations happen after a power outage event affecting only PSU's in slots A, considering a Power Stack of 4 members?

- Difference between Graceful and Immediate load shedding events is not clear.

 

Help with any of the above is highly appreciated. Thanks!

F.

 

3 REPLIES 3
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Fed Beginner
Beginner

Re: 3850 Stack-power questions

Any ideas or suggestions?

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Participant

Re: 3850 Stack-power questions

Hello Federico,

3850 Stack-power questions

  • 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.

Highlighted
Fed Beginner
Beginner

Re: 3850 Stack-power questions

Hi jkilleda,

Thanks for taking the time to reply, however I had read all this in official docos, but unfortunately it still doesn't answer my questions.

Cheers

Fed

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