We help IT Professionals succeed at work.

server hardware power supply unit

High Priority
Last Modified: 2020-02-10
Dear Experts
Servers having two PDU's and each power units connected to separate UPS if one UPS goes down server hardware will continue to work with other UPS, have following doubts
Does server hardware consumes power from both the PDU’s all the time equally OR  is there a concept that one PDU will be primary and if this goes down only then secondary PDU becomes active and this will keep the server running. please help me understand. Thanks in advance.
Watch Question

A lot of manufacturer's do things a little differently, but in the case of HP's you have afew options:

Of the two main options, there's some granularity in the High-Efficiency Mode:

  • High Efficiency Mode provides the most power efficient operation with redundant power supplies by keeping one power supply in standby mode at lower power usage levels.

  • Balanced Mode shares the power equally between both power supplies.

In addition, the "Auto" mode chooses between one PSU or the other as primary, depending on the serial number. It's a way to randomize the distribution in a datacenter situation with multiple servers.

reference: https://techlibrary.hpe.com/docs/iss/proliant_uefi/UEFI_Moonshot_103117/GUID-D7147C7F-2016-0901-0A69-000000000C2C.html
kevinhsiehNetwork Engineer
Servers have PSU (power supply unit), which may then plug into PDU (power distribution unit, which is usually like a giant plug strip).

At any rate, it depends on the vendor and the settings. The above expert summed it up very well. Draw could be roughly equal, or one PSU may be at significantly higher load. The reason for a PSU at higher load is that PSU are more efficient at greater load, so there is less wasted energy compared to running two PSU each at lower utilization.

Controlling PSU mode is usually in your BIOS settings.
EE Topic Advisor, Independant Technology Professional
I also agree that how it works does vary from server to server. However if you get the choice, make sure you set the power supplies so that half use one UPS as their primary and half use the other. Then test to be sure if one UPS fails, the other has sufficient capacity to give you the run time you want.