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When one of the two power supplies to a server is lost does it need to be manually 'reset' or will it automatically start working when power is restored. I can find no documentation about this so I would be very grateful if anyone can help me. The servers I am using are Dell Poweredge 2950, 2900 and 2800.

The reason I'm asking is that our servers are currently powered using standard household extension leads and I want to change then for the more reliable PDU's. I would like to be able to do this without having to switch off the servers.

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up vote 2 down vote accepted

No "resetting" is required and you don't need to power down the server to change the power cords as long as you change them one at a time. One PS is always active and the other is always passive. When the active PS loses power, the passive PS takes over with no intervention needed on your part. When you switch the cords the currently active PS will go passive and the passive will go active, so the server will never lose power.

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Just to clairify, when both PS are online the load is shared and balanced between both of them. There is no "active" and "passive" PS. I have confirmed this in the documentation and double checked this with a Fluke Tong tester. When one PS fails then the remaining PS will carry 100% of the load, however when the secondary PS is brought back online then the load is balanced between both units. – Richard West Nov 30 '09 at 14:22
@Richard West: Thanks for the clarification. I had always assumed, based on what I had been told, that the power supplies operate in an active-passive mode. My Dell rep confirms what you've stated regarding them operating in an active-active mode. – joeqwerty Nov 30 '09 at 15:34

You won't need to do anything manually to get the redundant power supply to work. Removing power from one supply at a time should allow you to move your power source without downtime.

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I've done this on several occasions. It should cause no issues.

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Thought i've not tried it on my dell servers, i think there should be no problems.

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