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Onboard Administrator (OA) power calculation

chuckk281
Trusted Contributor

Onboard Administrator (OA) power calculation

Tristan had a power question:

 

*****************

 

Hello,

 

Can someone explain how the OA calculates the enclosure power capacity to be 7400W in an enclosure with 6 x 2250W and AC redundancy mode set ?

The customer also indicates that the power capacity reported by the OA is correct when the blades are in stand-by.

It shows 6750W (3 x 2750W) with the servers in stand-by.

 

It changes to 7400W when the blades are powered on one by one.

 

Showall extracts are copies below.

>SHOW POWER

 

Power Mode: Redundant

Dynamic Power: Disabled

Set Power Limit: Not Set

 

Power Capacity:              7400 Watts DC

Power Available:                0 Watts DC

Power Allocated:             7400 Watts DC

Present Power:               3171 Watts AC

Power Limit:                 8998 Watts AC

 

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Info from Dan:

 

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Max Input power is 9000Watts which is 2250 x 4

So perhaps you are set in Power Supply Redundancy mode (N+1) and not AC Redundant (N+N)

 

But N+1 with 4 would indicate you have 5 PSUs online which doesn’t match your 6 below.

 

Anytime you see DC, that’s internal power and not wall power.

Anytime you see “Allocation” that’s how much the chassis thinks it could draw if every component went to 100% at the same time.

 

So this section is key:

Enclosure Bay Output Allocation:

Bay               Power Allocated (Watts DC)

-------------     --------------------------

Devices                   6520

Interconnects   +   380

Fans                      +   500

                       -------------

                              =  7400

 

So that says your blades think they could, combined, consume 6520W if they all went crazy.

Interconnects would take 380

Fans would take 500 (50W x 10 Fans)

 

Because 7400 is more than 6750 (2250x3), you would not have been allowed to power on Blade 16 and probably not 15 either.

So someone changed the Power Redundancy mode to N+1 which changes the allocation maximum, and then the last 2 blades come up.

This is not a bad thing, because there seems to be a wild swing between actual usage of a normal blade server and what we consider the Max/Allocation to be.

 

For instance, when you ran the commands, here is your actual usage:

Enclosure Input Power Summary:

Enclosure              Watts AC

-----------------      --------

Present Power             3170

 

So you can see from the wall, including some loss due to AC/DC conversion, you are only drawing 3170 which is way less than 6750 and means you are still technically N+N redundant.

But back to what I said before, either my math is off, or one of your power supplies is.

 

Actually, I wonder now if they are deregulating the number automatically.

 

5 PSUs (N) x 2250 = 11,250Watts

In North America, you are only supposed to use 80% of that consistently (you can spike higher)

11250 * 0.80 = 9000

So perhaps you don’t have only 5, you have 6 and the OA is doing the 80% rule automatically for you.

Because you showed below you most definitely have 6 and they are all online.

 

Hope that helps explain some of these numbers.

 

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