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What does the current distribution look like on a Dell PowerEdge R630 (or any for that matter) when using 2 power supplies?

I assume it will either draw continually from both, distributing the load, or it will favour one over the other. If the later, how does it decide which and is there a way to tell while it's running which that is?

Context for the question is I have a rack load of R630s all with dual-PSU and I'm wondering if one PDU has the current capacity to feed the rack if the other one goes.

Note: This is different to the previous question How do servers with redundant power supplies balance consumption? as it specifically asks about Dell R630s

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SimonJGreen
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3 Answers3

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I've found the specific answer to the distribution question now, so sharing here just in case others want it. According to the R630 Owner's Manual on page 99:

When two identical power supplies are installed, power supply redundancy (1+1 – with redundancy or 2+0 – without redundancy) is configured in system BIOS. In redundant mode, power is supplied to the system equally from both power supplies when Hot Spare is disabled. When Hot Spare is enabled, one of the PSUs will be put into standby when system utilization is low in order to maximize efficiency.

So in an R630, regardless of configuration, both PSUs will draw evenly except under very low utilisation where only one PSU will be used.

SimonJGreen
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It depends a bit on your server manufacturer and system settings, but check out the details at:

How do servers with redundant power supplies balance consumption?

It sounds like your real question is: how do I size/plan my power circuit?

If you lose a leg of power, assume full power draw on the surviving circuit.

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ewwhite
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I did small practical investigation, as was interested in this question also.

So if I have two PSU 750W each, so we have cases:

  1. Load balance, double power configuration. Dell allow them to work in parallel and total power will be double. The Power Monitoring will indicate:
Power Supply Redundancy - Disabled

1974 Watts - Failure Threshold


Power Supply Unit Readings
PS2 0.6 240 
PS1 0.6 240

To achieve this, both PSU must be powered and Overview > Power/Thermal > Power Configuration > Power Configuration Redundancy Policy should be set Not Redundant

I suspect that Max power, Failure Threshold is in peak Watts, as nominal power would be 1500W

Assumption two, that setting Hot Spare will have no practical effect, as removal of power from one of PSU when system power consumption is more that single PSU can handle, results in server power off.

  1. Single PSU failure resistant, load balance configuration.

To achieve this, both PSU must be powered and Overview > Power/Thermal > Power Configuration > Power Configuration Redundancy Policy should be set Input Power Redundant

The Power Monitoring will indicate:

Power Supply Redundancy - Full

980 Watts - Failure Threshold


Power Supply Unit Readings
PS2 0.6 240 
PS1 0.6 240

This means both PSU are in use in parallel, handle half the server power load. I would say its beneficial in case when you put PSU load point at good efficiency point, when 2 PSU work in highest efficiency range, still in case of failure, one can handle the load, but out of best efficiency range defined for that PSU.

  1. Hot Spare configuration.

To achieve this, both PSU must be powered and Overview > Power/Thermal > Power Configuration > Power Configuration Redundancy Policy should be set Input Power Redundant

Hot Spare set to Enabled

The Power Monitoring will indicate:

Power Supply Redundancy - Full

980 Watts - Failure Threshold


Power Supply Unit Readings
PS2 0   240 
PS1 1.2 240

As my system power draw is quite small, PSU in load balance configuration work not in optimal efficiency range, thus in my scenario single PSU working in more efficient range and second PSU in standby (power saving) is resulting in around 10% less Total power consumption from outlet. Thus more energy efficient.

Arunas Bart
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