Archive for February, 2010

Flat Rate or Metered

February 9, 2010

How do you prefer to pay for Data Center power?

When choosing a colocation facility, one thing to consider is the format the provider uses to charge for power. It is important that the provider you choose to colocate with uses a power pricing format that is compatible with your expected deployment to avoid paying for power that you do not need or even worse could not be effectively cooled.

In general terms, most data centers will use either a FLAT RATE per circuit or a METERED power pricing model. How do you know which is best for you?

If you ask IT infrastructure professionals which model they prefer,  most will say they prefer a metered model as it implies that you pay only for the power you use. Be sure to read the fine print and make sure you are 100% familiar with all the potential factors that  impact your monthly power cost. A couple things you might want to verify are:

  • Monthly Minimum – typically in a metered power model their will be a monthly minimum of usage applied to your power bill. A common minimum is 40-50% of the breakered power total. This protects the data center from delivering large amounts of breakered power per cabinet and  having the client using only a small percentage. This is even more important when you have more than one primary circuit per cabinet. For example, let’s say you have leased a cabinet equipped with 2 x 30A/208V  single phase, primary power circuits in an A + B configuration delivering 6.24KW per circuit for a total of 12.48KW cabinet. The standard allowable actual draw to avoid potentially tripping circuit breakers is 80% of  the breakered total or 9.98KW.  In that cabinet, you deploy a blade server chassis with dual power supplies that draws a total 4KW with the intent of drawing 2KW from each of the two primary power circuits allowing you the ability to draw the entire 4KW from either circuit should you lose a power supply or a PDU.  In this case, 2KW actual draw is roughly 32% of the breakered total of 6.24KW per circuit. If the provider has a 50% minimum, that is 18% per circuit or 2.25KW of unused power you will be charged for. At an example rate of $185 per KW that is $415 per cabinet for power you will not use.
  • Max Actual Draw per Cabinet – It is common for an end user to expect additional power to be available when a metered power pricing format is used but that is not always the case. For example, you lease a cabinet as described above with 2 x 30a/208V circuits and you are drawing about 6KW,  approximately 50% of the breakered total. Logically, you assume, that you would have at least an additional 30% or 3KW+ of available power per cabinet, however be sure to check your provider’s Max actual draw per cabinet. You may be surprised to learn that they cannot effectively cool more than the minimum, removing any advantage a metered model may provide. 

When a flate rate per circuit model is in place, there are also several important factors to consider:

  • Cooling Capacity- As is the case in a metered power model, the maximum actual draw per cabinet that can be effectively cooled is an important factor when choosing the appropriate amperage and voltage for your cabinets. A rule of thumb is that the maximum actual draw is 80% of the breakered power total. For example, a 20A/110V power circuit will allow you to draw up to 1.76KW or 80% of the 2.2KW breakered total. Most data centers can easily cool this type of density but  when you get into the larger circuits or multiple primary circuits per cabinet you may run into a limit that can affect your potential for expansion and the ability to fully utilize your available cabinet space. Be sure to verify the limits before planning your power deployment. You do not want to end up paying for power you will never be able to draw.
  • Scalability – Let’s say you lease a cabinet and it comes with a single 20A/110V power circuit. You load in 10 of your 12 total servers and realize that despite your estimated power utilization calculations you have maxed out the circuit and will require an additional 20A/110V circuit. This is where flat rate can be a burden. Let’s say the flat rate cost of the circuit is $250 per month and you have to add an entire new circuit to power the last two servers, that is not an effective use of available power and will result in additional cost. A better plan may have been to chose a provider that offers metered power or simply to have started with a 30A circuit which would have been a better fit.

Regardless of what power pricing model is right for you, what is most important is that you select a provider that is willing to work with you to help you establish the most cost effective solution without compromising any reliability. At 360TCS we work with each client to find a solution that fits. We are flexible and willing to utilize different pricing models to meet our client’s needs and meet our stated goal which is Total Customer Satisfaction.

 http://www.360TCS.com

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