Do You Know What Your Datacenter Costs to Operate?

This isn’t going to be a deeply technical post, but it’s something I run in to a lot.  Most IT organizations don’t know what it costs them to operate their data centers.  It’s really not their fault.  Usually they never see the power bill for the facility.  The only time they put much thought in to their power consumption is when they need to pull new circuits or hit a wall with their cooling.  It’s better to put thought in to this early rather than wait until you can’t do something you need to do.

First, if you’re interested in power and cooling for data centers I highly suggest you read the EPA’s report to Congress.  It is available here.  It goes in to some excellent discussion around future data center growth and the power we’ll need to meet it.  It’s also a good read as many people use it as the “common ground” when discussing power and cooling and it has some great statistics in it, such as:

• “The energy use of the nation’s servers and data centers in 2006 is estimated to be more than double the electricity that was consumed for this purpose in 2000.”
• “Under current efficiency trends, national energy consumption by servers and data centers could nearly double again in another five years (i.e., by 2011) to more than 100 billion kWh, representing a $7.4 billion annual electricity cost.“
• “If current trends continue, this demand would rise to 12 GW by 2011, which would require an additional 10 power plants.”

Okay, first step is to know how power is bought and sold.  Electricity is sold by the Killowatt hour.  For example, you have a server that uses 1,000 watts, which is 1 Killowatt (1KW), and you run that server for one hour.  It has used 1KW/h.  The average cost for electricity in the United States is 10 cent per KW/h.  So to run that server for one hour would cost you .10.  Now look at a rack of servers that use 10KW of power.  You run them for a year.  What does it cost?

10KW (rack total) * 8760 (hours in a year) * .10 (10 cent per hour) = $8,760 per year.

That’s a lot…but it gets worse.  You don’t just pay to power data center equipment but you also pay to cool it back down.  The cost to do that varies as some cooling systems are more efficient than others, but in most cases a good estimate is to just double the power numbers you came up with to run the equipment.  Some systems are worse and you use a 1.5 multiplier.  In our example it would cost a total of $17,520 to power and cool that one rack of gear.

The next challenge to accurately getting your numbers is to figure out how much power your equipment actually uses.  A lot of people make a big mistake here and look at the number on the back of their power supplies.  That’s wrong.  That’s known as the “plate number” and tells you the maximum power that the power supply can handle, not what the server is actually doing.  To get a more accurate count you need to do some work.  You have a couple of options.

The first option is to use a power calculator from your equipment vendor.  EMC, Cisco, HP, Dell, etc all have pretty good calculators on their sites.  They provide a good estimate if you input good information.

The second option is the most accurate.  Use a power meter.  It’s more work since you have to physically test the equipment but you get an accurate read on YOUR equipment under YOUR load.  The amount of power a server draws will vary GREATLY depending on the load put on the system.  You can start witha  cheap Kill-a-Watt device like I use around my house to answer my own curiousity or a more expensive unit with logging and graphing.  Just make sure to find one that can handle the amps your equipment pulls.

So what can you do to reduce these numbers?  Buy efficient equipment and virtualize.  Not all servers are created equal.  More importantly, not all power supplies are of the same efficiency.  A server that costs a bit more may have a 90% efficient power supply while a cheaper one may only be 80% efficient.  Which one really costs less in the longterm?  Virtualization is an easy win for saving power and cooling.  Consolidate equipment and cut down on the things in the data center you have to power and cool.  This goes for those islands of storage you still have, too.  Move to a consolidated storage approach and reduce the number of spindles in the data center.