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10-30-2014 07:16 AM
Question about Power Management in C7000
Eric had a customer question:
We have currently a problem of power management of 2 enclosure installed in a customer DC.
On the first enclosure :
The enclosures are connected each on separate power lines on different PDU : no problem here.
But, during a test about PDU failure, after making one PDU power down and up after some minutes, and doing the same test on the second PDU, the 3 power supplies attached on this second PDU were unable to power up even if the customer eject them and plugin again.
After one week these 3 power supply have been tested and are working perfectly… seems that they were put in save mode or something like that.
But the most important problem here is that during this failure on PDU 2, even if the PDU1 was up, with 3 power supply running, some blade has been powered off. The OA information tell that the power is not sufficient for the blades but 3x2400W is far more than needed for these blades …
On the second enclosure, a mistake in power connection to the PDU makes the PSU 1,3,5 connected to the PDU1 and PSU 2,4,6 connected to PDU2.. this is not what HP support.
So last week the customer has made the change by switching PSU 2 and 5 to the correct PDUs.
Again by doing so, some Blades has powered off…
Someone for HP support told that the problem is due to the N+N mode because a failure of one PSU can create a situation where only 2 PSU only are used for the blade and that could be insufficient.
So the best practice is to use the Non Redundant mode …
Any idea about this power supply configuration as the right best practice please ?
In a N+N configuration in case of PSU failure what’s is the action the OA will do ?
Same question with non-redundant.
Info from Dan:
N+N AC Redundant mode is mostly around Power Allocation.
In N+N you only get N worth of power supplies added to the allocation.
That is 3 power supplies which matches the Left vs Right design of the c7000 (123 vs 456)
In N+1 (Power Supply Redundant) you get the same, but now N is 5
In N (Not Redundant) you get 6
The problem with using N+1 or N mode is that now the OA will NOT prevent you from powering on a blade if that blade will put you over the top of what 3 power supplies can handle from an allocation perspective.
So you are just setting yourself up for failure if a single PDU Circuit goes down.
As far as your Swap of PDU 2 and 5, you killed 33% of the incoming power on BOTH sides of the c7000.
This is why some blades powered down as you now only had 2+2 instead of 2+3
What you should have done is:
Find an extra unused C19 plug somewhere else
Move the cable from PSU 2 to this other plug and wait 2 minutes for it to be powered on and fully recognized.
Then move the cable from PSU 2 to the spot where PSU 2 used to be. Again wait 2 minutes.
Then move PSU 2 cable from Extra spot to where PSU 5 used to be.
This series of steps ensures that at least 1 side of the c7000 always has 3 PSUs active.
As far as power not being sufficient, you need to understand the difference between actual utilization and Power Allocation. Errors about not enough power to turn on blade have to do with Power Allocation and should only happen with a full blade chassis of 16 blades with very high specs.
This is why we now offer 2650W PSUs for the c7000.
So you can get an extra 750W (250W x 3) boost over the previous 2400W model and give you enough power for blade 15/15 to power on.