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Hardware Thread, UPS Wiring. Both PSU's powered through UPS or just the one? in Technical; Hi, When i first started here they had both PSU's going through the UPS. When the UPS dies it dropped ...
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    UPS Wiring. Both PSU's powered through UPS or just the one?

    Hi,

    When i first started here they had both PSU's going through the UPS. When the UPS dies it dropped the server.

    Is it best to have both PSU going through the UPS and just say that its rare that it fails or do you have only one going to the UPS and one going direct to mains?

    Many thanks,

    Dan.

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    glennda's Avatar
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    I would put something between the mains the server which does Surge protection but yes as long as one PSU is in the UPS and you don't have a second then the mains would be fine as long as its surge protected.

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    dany2010 (3rd October 2012)

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    m25man's Avatar
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    In a dual PSU scenario one of the PSU's is on hot standby not drawing current. So in theory both should be plugged in to your UPS's
    If not, when your power blacks out you will loose the PSU on the mains but if the hot spare is the one on the UPS it will need to fail over to it this can have unpredictable results especially when the UPS suddely switches in to a full load and the outputs are very coarse square or sawtooth.
    I have seen many HP servers slam dunk in this configuration.

    This happens mostly when the number of protected outlets exceeds the number needed by the servers. So I would make sure that you have enough outlets by using the correctly rated PDU connected to the UPS's with both of your Server PSU's being fed from the UPS.

    We all do it, we all try and run the UPS requirements on the redline and it doesnt work very well. Give yourself plenty of breathing space never more than 50% load and plenty of runtime.

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    dany2010 (3rd October 2012)

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    Its fairly pointless to have the redundancy of 2 power supplies and then connect them both to the same device which can fail. Ideally you want 2 ups's although most of the time this isn't possible so we normally go one psu into ups and the other into a surge protector off the mains.

    Steve

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    dany2010 (3rd October 2012)

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    mrbios's Avatar
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    Each PSU connected to a separate UPS is the best scenario

    If not then one PSU connected to UPS and one connected directly to the mains (plug the latter in second so the UPS on is being used primarily, and have some form of surge protection on the socket) this way you're covered no matter what dies.

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    dany2010 (3rd October 2012)

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    Thanks all. Put one through the battery backup plug and the otherthrough the surge protector.

    Not 100% safe if one PSU goes but we are in and out all day so hopefully would see the warning symbol if one went.

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    plexer's Avatar
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    I don't think they are all run as hot standby.

    Ben

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    Quote Originally Posted by plexer View Post
    I don't think they are all run as hot standby.

    Ben
    Ben you are correct, not all configurations run in a standby mode.
    HP Proliants have High Efficiency or Load balancing options in the BIOS and depending on the configuration this is known to be a cause of unpredictable reaction during a blackout condition.
    It may be worth Proliant users check their configurations to ensure the best option is enabled for their needs.

    However, switched mode PSU's get even more twitchy with age as capacitors degenerate over time and their ability to cope with sudden AC loss becomes a game of Russian roulette regardless of config.
    I had a real problem with this and HP were adamant that the coarse output of my UPS was to blame for my PSU issues.

    steveg's idea of dual redundant UPS is a good idea and saved my bacon this week when our builders took out the main breaker for the entire building kept my SAN running all through whilst everything else eventually ran out of steam much sooner than was expected!

    This publication may be of interest to those wanting to review their existing power supply configurations.
    http://www.bitcon.be/wp-content/uplo...TC091110TB.pdf it explains the implementation of redundant PSU's in HP Proliants and the two options.

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