We have data center running more than 2000 servers. We are planning to shutdown the servers on a weekend for cost cutting purpose. How can we calculate which servers are consuming more power in the data center so that we can shutdown those many servers only . What is the best way to determine power saving on hourly/daily/weekly basis.
You can get amp meters to measure the power. or you could take meter readings from your electric meter.
The best way to get good readings is to do this for 24 hours. Not just a few hours. (You mentioned the weekend) and that obviously is a good time. But if you are able to get 2000 servers available for downtime at a weekend, do you need all of those servers?
Use PDUs [See footnote 1] that provide metering capabilities, such as these Metered Rack PDUs from APC. Monitor the PDU using software-- APC provides software which allows continuous power monitoring, and there are other options. Your best bet is to monitor power consumption trends over time.
Some PDUs only monitor down to the circuit which will still allow you to localize servers with high power consumption. Some of the newer PDUs allow monitoring all the way down to the outlet.
From what I know, a typical Datacenter spends more then 50% of it's energy budget on cooling. Computers generate heat, which then needs to be cooled by energy-intensive methods. Heat is one of the primary drivers of energy cost. Nearly every major air-handling vendor offers equipment which allows the company to monitor the power consumption.
Really, there is an entire industry out there which can help you monitor power consumption in your datacenter.
Footnote 1: PDUs are fancy power strips. Some people, especially electrical contractors, use the term "PDU" to refer to the big box which distributes power from the mains or the UPS.
Its mostly the CPUs that are consuming power. You can look up their wattage in their specs. But they will be most propably be in low-power mode when there is nothing to do. So look up these specs as well (it depends on your OS which power-saving mode will be activated).
Additionally there is the wattage used by the disks.
So all in all the fastest multi-cpu-monsters with lots of internal disks are probably the power-eaters.