Energy efficiency
Comments on corrected results
If conditions had been identical for the ‘Before Cleaning’ and ‘After Cleaning’ periods, the power and energy savings would simply be the difference between the two sets of measured results. However this was not the case, because both mains supply voltage and CPU processing load average values differed for the two periods. The University’s analysis accordingly has adjustments to allow for these differences.
In fact the mains supply voltage averaged 244.7 VRMS for the first week, and 244.6 VRMS for the second. Observation indicates that as the supply voltage drops so the power consumed increases slightly – about 0.17%, or 0.15 W for the recorded 0.1 VRMS decrease. This was compensated for by recording a corrected power consumption after cleaning of 88.59 W, and a corrected weekly energy consumption of 14.883 kWH.
Differences in the CPU loading before and after cleaning the server were also noted. Four aspects of the load were monitored throughout the study: CPU Usage, Load Average, Memory Usage, and Network Traffic. These characterize the server performing its in-service workload. By correlating and weighting each of the CPU, Load,
Memory and Network Traffic data figures, the weighted aggregate load after cleaning was 8±1% higher than before cleaning. A direct relationship between processing load and power drawn cannot be inferred because this depends on the precise configuration of the rack, PSU, UPS (if any), disk and other components. Also, the efficiency of the system components will vary as a function of power.
However, taking into account relevant factors, this extra load is estimated to contribute around 1-2% to the power consumption. This leads to the final “Corrected for CPU Load and Supply Voltage” results shown in the Table above.
Other relevant factors Southampton University’s Review commented that the methodology used in the survey was good “since measurements were actually performed on a live running server with a live running load and the actual dirt it has accumulated over time in situ”. However other data centre scenarios could yield different energy saving results.
The tests were performed within a large, highly professional co-location facility that relies on providing processing power to third party users. Accordingly, the operators expend time and effort in maintaining a clean environment, because their business
Corrected Before Cleaning Power W
Energy kWH/week Corrected Power
Saving, W Corrected Energy Saving, kWH/week
88.79
14.917 -
- After Cleaning For Supply Voltage
88.74 14.91 -
- Table: Single server power and energy consumption before and after cleaning Winter 2010
www.datacentresols.com | DATA CENTRE SOLUTIONS | 25 88.59
14.883 -
-
For CPU Load+ Supply Voltage
87.14 14.64 1.65
0.28
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