Data Centers

Sharpshooting data center power? Check UPS

If you are like many environments in that you are power constrained, you will take any efficiency you can get. In this post Rickatron takes a look at UPS energy efficiency.

Too many times when we design data centers, we monitor power consumption at the device only. This could be from a storage array or a server in many cases. Sometimes we may also check in on the power distribution units (PDUs) that may be in use within a rack as well. But do we look closely enough at our uninterruptable power supplies (UPSs)? Chances are, we may find efficiency there if we have to be constantly mindful of data center power consumption. Recently I read a blog by Troy Miller that got me thinking about this very topic.

The logic here is that if the UPS unit is very efficient, it is possible that the “overhead” associated with the power protection can be reduced. That may be that extra few percent of improvement needed in the power- (and space-) constrained data centers of today.

Now, to set the record straight, all UPS devices are not created equal. There are three main types: VFD (line interactive), VI (standby) and VFI (online double conversion). These types were enumerated recently by APC, leaders in the UPS space. There is a certain amount of competitive tension going around about this topic, and the fact that all devices are not created equal is important.

The VFI type is preferred by many as AC power is received, charges the battery as DC, and then the battery power is converted to AC for the devices to consume. In this way, there is no interruption if there is a power loss because the second stage is untouched from the battery.

In fact, some electronic devices in the data center may require a certain type, such as the VFI. In my experience (albeit quite a while ago), I had a telecom system that required that type of power conversion. The system provided voicemail for my office and for some reason, it was sensitive enough to detect normal power fluctuations if a regular UPS (VFD type) switched from AC to battery. Other sensitive systems may require power conditioning, which I have experience with as well. In fact, I’ve even put power conditioning in front of a UPS unit. That gives very clean and reliable power, yet it requires a high power overhead to do it.

The takeaway is to know the devices in your data center, big or small. It also may be worth implementing high efficiency UPS devices that do VFD for one range of equipment and another group that does VFI for the most critical areas. You can get an additional power efficiency via the UPS if you need it.

About

Rick Vanover is a software strategy specialist for Veeam Software, based in Columbus, Ohio. Rick has years of IT experience and focuses on virtualization, Windows-based server administration, and system hardware.

4 comments
techrepublic
techrepublic

The reason VFD (line interactive) UPSs can still upset some connected devices is that until there is an under or over voltage condition, the incoming mains supply is simply fed through to the load. This means that the UPS does not reduce the efficiency of your data center. Unfortunately when an under or over voltage event does occur, big high current relays switch the AC outputs from the incoming mains line to the output transformer which generates a nice clean 50/60Hz AC power signal. The relays can take varying amounts of time to switch over and settle (10-50ms = several mains AC cycles). Therefore your connected hardware must have large enough reservoir capacitors to sustain a steady DC level inside your equipment even in the event of brown-out conditions. The always online double conversion UPSs do not suffer this problem as they are always converting from AC to DC to AC (with the battery in between). As is true with most things in life - you get what you pay for!

b4real
b4real

UPSs may hold a problem yet be hard to see.

albksi
albksi

we had some recent problems with a our power supply system, tried filtering the power through a stabilizer, a ups and a second ups then the PDU on the server rack. However we still have some issues with some of our servers. Could it actually be the UPS solution is wrong or simply the servers faulty. My honest guess is despite the UPS solution power problems may persist, is this true?

techrepublic
techrepublic

Hi Albski, See my post "Line interactivity".