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N+N Power redundancy issue?

 
chuckk281
Trusted Contributor

N+N Power redundancy issue?

Steve had a power question and issue:

 

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We have a C7000 with 12, BL460c Gen8 blades and six, 2400W Platinum PSU (using AC Redundant). Over the weekend there was a power issue on the A side, which the chassis coped with. However two of the three PSU’s on that side have blown. We now have a chassis with one PSU on A side and three on B side. To my understanding all three B Side PSU’s would be active?

 

Yesterday evening one of the blades (slot 9) has been powered off and is claiming ‘Insufficient Power’. However, Power subsystem shows two of the four working PSU’s in Power Saving mode!!! How can they be in power saving when the system has insufficient power to restart one of the blades?!

 

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Reply from Torbjorn:

Total power allocated is 5037W. Total available power in N+N with 4 PSUs active is 2450*2 = 4900W. You have already over allocated power and are not allowed to allocate more power until the issue with PSU 1 and 2 are fixed. If you shutdown anything else you will not be allowed to power it back on as you have already allocated more power than you have available (5037W vs 4900W).

Then you only have 1 PSU on A side satisfying the N+N policy set in OA which means you only have 2450W available to allocate. Either way you need to replace both PSU 1 and 2 to get enough power available to allocate for booting another blade or change the current power redundancy setting. Every time you boot a blade it will always verify that it has enough power available to keep the systems running at the desired power redundancy level with the server using the maximum amout of power it possibly could. However it will never shut down a blade to restore a requested redundancy level, only preventing you from making it worse.

 

At current usage you would be okay to run the entire system on only 1 PSU (only 1289W currently in use), but you would not be allowed to boot any new blades in this scenario either without changing power redundancy mode.

 

 Input from Thoa:

With 12 blades inserted we would need 3 zones , in an N+N config we would require all 6 PS active.  Perhaps you can have the customer change to n+1 for the time being and PS 6 can sit in for the two missing ones.

 

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