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Measured using a ‘Classic’ Current Cost unit (a clamp ammeter with short-range packet radio interface), wired up to a server’s RS-232 serial port using a home-made cable. Data is received in an XML format, which a small Perl daemon receives and then inserts into an RRD. The graph is SVG, generated on-the-fly by RRDtool from a Lua CGI script.
Household power consumption rises and falls each day, overall. Large spikes usually represent the washing machine or another large appliance operating for a period of time. The 1-hour resolution here is too coarse to show the higher, short-duration spikes of an electric kettle, or refrigerators that switch on/off more frequently. A desktop PC or television causes a large step up or down in the readings.
The blue line is an estimated theoretical minimum, comprised of appliances expected to draw power 24 hours a day (such as servers and networking gear). If consumption does not drop down to this line in the early hours, then maybe other appliances have been left switched on.
Data retrieved from an APC SmartUPS’s USB interface using apcupsd, with a Dash shell script inserting readings periodically into an RRD. The graph is generated by a different (older, less efficient) method than the graph above: a PHP script invokes the rrdtool CLI program to update a PNG image file on-disk if needed, then the file’s contents are served by PHP.
The readings indicate the power consumption of a Sun Fire v20z server: twin dual-core Opterons, with CPU frequency and voltage scaling enabled. Power consumption increases when one or more CPU cores are busy. Also an external RAID enclosure with 5 Fibre Channel disk drives. Both the server and disk enclosure increase their fan speeds in hot weather and an increase in daytime power consumption can sometimes be seen.
An external LTO-2 Ultrium tape backup drive operates on weekends but has its power manually switched off at other times. The unit draws over 30 Watts when idle or waiting for a manual tape change, and over 50 Watts whilst writing. Even more power is used by the server when writing backups, because it occupies a CPU core for compression and another for encryption (a pipeline with a large enough buffer in between to facilitate task parallelism, so it can complete faster).
A blue line also shows the UPS battery charge as a percentage. If emergency power is ever needed, the line falls sharply, then rises again slowly as it is recharged.