Graphing kWh from switched PDU device

[technicidat]

Hi,

I have searched the forums for similar posts but have come up empty handed..

Perhaps someone can provide guidance.

We have many switched PDU devices (manufacturer is ServerTech) in our customer racks and we use these at present to bill customers in a fairly approximate manner based on how many Amps they are drawing.

Of course there are some limitations and problems with doing this (which I wont go into) and I want to move to a kilowatt hour (kWh) based measurement and billing system.
This is what our colocation provider bills us on so it makes even more sense..

The units provide some SNMP data when polled. Most useful OID's being:

- Voltage
- Amps (draw across all outlets)
- Watts

Watts can be calculated from Amps x Volts but they are doing this on the unit already which is useful.

My questions;

My maths so far:
e.g:

220volts x 8 Amps = 1840watts
1840watts / 1000 = 1.84kilowatts


24hours x 365.2425 days per year = 8765.82 hours/year
8765.82 / 12 months = 730.485 hours per month

Average hours per month: 730.485

1.84kw x 730.485 hours = 1344.0924 kilowatt hours per month


1. Is this calculation correct?


This makes sense when the usage is constant, but how to graph this when the figure changes and the measurement must be graphed and added over time.. Leading to my second question:

2. How can I graph this into a graph that we can use to bill on an absolute number of kWh used per month?



Any help would be much appreciated, I'm not sure where to go from here..

Thanks.

Regards.

[BSOD2600]

1) on quick glance, math looks correct... but how can you assume from a single poll they're using X killowatt hours per month? As servers go idle/hot, their wattage obviously changes. Why not use/graph the real time usage?

2) For graphing/reporting, several things. Consider looking to use the ReportIt plugin or maybe the ISP Billing Script - Nth Percentile and Bandwidth can be adopted for your needs.

I'd suggest making a snmp data query to collect the data. Once you have the data pulled and stored in the rrd file, you can create a simple CDEF to do the math and then graph it.

Also be very aware of rrdtool consolidation. You'll probably want to change your default rrd settings so you extend the history -- otherwise in a few months the old data the graphs will show will be incorrect.