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08-26-2015 06:38 AM
08-26-2015 06:38 AM
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
************
Info from Dan:
************
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.
***********
Other comments?
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