These parts are: electrical service, backup generator, uninterruptible power supply, automatic transfer switch, power distribution units, power monitoring, and power consumers, such as servers, routers, and switches.

The main difference between power for devices in the datacenter and other types of power service is that a power loss in this situation can be a really big deal. These devices need power that is always on, even in a storm, to function properly. Making the datacenter stay on when the power from the electric company falters takes some special design considerations.

This is how the pieces fit together for our environment:

Normally, all of the power used by the datacenter comes in through one or more electrical services which are either part of the building’s power system, or are dedicated to the datacenter.

This electrical service is pretty reliable, but it can and does fail. Bad weather, natural disasters, human error, road work, and scheduled maintenance can all turn the power off for a time. In some places it is more rare than others to have an electrical outage, but no place is immune. A generator, transfer switch, and uninterruptible power supply (UPS) will keep the datacenter on while the power grid is off.

The UPS is a battery backup for the electrical service. Our datacenter uses a double-conversion, or “online” UPS. Double-conversion means that the AC power coming in from the electrical service is converted to DC power to charge the batteries, and then the DC power from the battery strings is converted back to AC power to power the datacenter. This method has some pros and cons. Since power is always supplied from the DC bus the batteries attach to, defects in the incoming power are smoothed out. During the conversion to DC and back to AC, voltage spikes and dips are corrected.

If the electrical service voltage goes too low or too high for a period of time, the load on the other side of the UPS should never see a change in the power it gets. If the electrical service drops offline for any reason, the UPS keeps providing power from its batteries without any interruption. Which is why it’s called uninterruptible.

Double-conversion comes at a price. Converting the power to and from DC, running the UPS itself, and keeping the batteries charged all take some power. For a typical UPS, this all adds a little more than 10% to the total power that goes through it.

When the electrical service goes out, the batteries power the data center forever, and they are not supposed to. This is where the transfer switch and the generator come into play. The transfer switch really does two jobs. First, it watches the grid power and tells the generator to turn on when there is a problem and to turn back off after the power stabilizes. Second, the transfer switch actually switches the feed that goes to the UPS from grid power to generator power and back when it is time.

When the backup generator gets the signal, it starts up and begins producing electricity. This usually takes a few seconds to a few dozen seconds, depending on the type of generator. Once the generator is running and the power coming from it is stable, the transfer switch connects the UPS to the generator instead of the grid. A while after the grid power comes back on and looks stable to the transfer switch, it connects the UPS back to grid power and tells the generator to shut down.

Also worth mentioning, even though it is not exactly part of the power system is the cooling. Power and cooling go hand-in-hand because all of the power that is consumed in the datacenter turns into heat which must be removed. The size and design of the cooling system is directly related to how much power the systems it will be cooling will use.

Typically, the cooling system is connected to generators, but not to a UPS. The pieces of the cooling system don’t suffer (much) from a power outage of a few seconds the way a server, firewall, or storage system would. It would be inefficient to run that extra power through the UPS when it is not needed. The lights are treated the same way. You’ll get by in the dark for a few seconds while the generator comes online. The servers are more picky.

From the UPS, getting the power to the servers should seem familiar if you are comfortable with how your home electrical service works. Here goes. From the UPS, the power is distributed by PDUs to the individual equipment racks. The PDU is a breaker panel with some additional features. Each rack gets power from one or more electrical circuits,which all connect back to breakers in the PDUs.

In our data center, each PDU also contains a transformer to convert the 480V Wye electrical service to the 120V single-phase circuits we deliver to each rack. Each of these circuits ends in an outlet that one or more rackmount power strips (also called PDUs, thank you very much) plug into. The equipment in the rack plugs into those power strips.

So in short, the transfer switch tells the generator when it is needed and connects the UPS to it when the generator is ready. The UPS smooths out the bumps so that the servers in the datacenter never notice a thing. Of course, every last part of the system is a little more complex than I have outlined here, but that’s how summaries go.

ipHouse is working hard to position our network and data center for the future.  This fall, we initiated a huge virtualization project. By using high-performance, efficient, virtual servers, we have been able to reduce the total number of physical machines used for hosting email and web services without impacting performance. Mike, our CTO, has been blogging about the virtualization project in his multipart series, “Virtualization and the ISP.”

Of course, virtualization is only part of the solution. IT departments need to think about the power consumption vs. performance of every machine on their network and every machine they are thinking of getting. Decommission machines that are no longer needed. Replace outdated energy hogs and stop getting more machine than is needed for the task at hand.

For years, data center and colocation power and cooling costs have been hidden or ignored. ipHouse is working to fix that. We are looking at both the power used by our equipment and the power consumed by colocated equipment. Colocation pricing is being revised to have a power consumption component. We want customers to consider power when they are choosing servers. We are also encouraging customers to take another look at their network assumptions. Especially with virtualization, separate services do not necessarily need to be on physically separate machines. 

If you are considering a move to a more energy efficient network design and want a second opinion on server specs and choices, let us know. We have been helping customers make infrastructure decisions for more than a decade and want to make sure you make the right choices for your organization.