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What you can do to ensure proper delivery of power via a UPS

Selecting an improper server room UPS or poorly maintaining a UPS can lead to UPS failures and data loss during an outage. Scott Lowe tells how to determine the proper UPS for your equipment load and how to maintain that UPS once you've installed it.


A UPS is your server room's lifeline in the event of a power-system failure, but many organizations either have insufficient sized UPSs for their equipment or forget to maintain their UPSs and end up with dead or low batteries. Either scenario can result in data loss and permanent hardware damage from servers crashing during a power outage, because the UPS wasn't able to keep systems running.

In this Daily Drill Down, I will explain how to make sure your UPS is prepared to power your servers when you need it by verifying its load rating, performing regular testing, and implementing scheduled maintenance of its components.

Power to the people
For the purposes of this Daily Drill Down, we’ll focus on the UPS in the server room rather than the smaller units used for workstations. While a workstation UPS is a good idea, having a UPS in your server room is absolutely essential. You will find, however, that many of the points made in this Daily Drill Down apply to workstation UPSs and server-side UPSs.

Selecting the proper size UPS
Because a UPS can be a major investment, it's important that you select the UPS that best fits your server room's needs. You must make sure the hardware the UPS will be protecting works with the UPS. Also, ensure that the equipment connected to the UPS won't cause the UPS to overload. You should also make use of the UPS' features that automatically shut down noncritical equipment in the event of a power failure.

You should purchase a UPS based on several factors, such as its included monitoring software, support, cost, and reputation. The most important factor, however, is probably its load rating, which is rated in volt/amps (VAs). The load rating determines how much equipment the UPS can support. Almost all server-room equipment has a rating listed somewhere near the power supply that indicates how much power the equipment draws. This rating is generally configured on the high end to ensure that a piece of equipment's power consumption isn't underrated, so it’s a safe number to use when determining how much load it will place on a UPS.

Unfortunately, manufacturers rarely state how many VAs a piece of equipment draws; they usually express power consumption in terms of watts. This leads to a problem, because watts don’t translate directly into VAs (i.e., 100 watts isn’t equal to 100 VAs). To determine a safe VA rating, you would need to include an additional Power Factor. The Power Factor is sometimes provided by the manufacturer but if not, it is safe to use 1.2. So to determine a more accurate VA rating, you would use volts * amps * PF (or 1.2 in this case) = VA rating.

But what if you are not given the amps drawn (for a piece of equipment) by the manufacturer? How do you make this calculation?

For example, suppose you have a Cobalt RaQ 4, and the documentation indicates the following power is drawn:
  • 60 watts
  • 240 volts

To calculate the VA rating, you'll first calculate the amps needed using the following formula (Please note this formula is only an approximation. To get an exact calculation would require a lengthy study of electronics and physics.): amps = watts/volts. So to find out the approximate VA rating for this particular piece of hardware, you would conduct the following calculations:
  1. Amps = 60 watts/240 volts
  2. Amps = .25
  3. Approximate VA = 240 volts *.25
  4. Approximate VA = 60
  5. VA = Approximate VA * PF (or 1.2)
  6. VA = 72

To determine what size UPS you need to purchase, add together all of the VA ratings of the hardware you want the UPS to protect. Compare those VA number totals to the UPS rating to make sure the UPS can handle that total load. Make sure the UPS rating has a little room to spare above and beyond the VA rating totals, which will ensure that the UPS can handle subtle power fluctuations. This also keeps the UPS from being drained at full capacity, which can shorten its life.

To see how you might calculate whether a Tripp Lite BC Personal 200 UPS System could handle a load of RaQ servers, you would take the VA rating for the UPS and compare that to the total VA of your servers. This particular UPS has a VA rating of 200 and in an ideal situation can provide power for up to 15 minutes. To max out this UPS, 2.7 RaQ 4 servers would have to be attached (2.7 RaQ 4 servers, each with a 72 VA rating, add up to a VA load of 194.4). Of course, it's unwise to run a UPS at capacity if it's supporting a server hosting mission-critical applications. You should never take a chance that a UPS will fail, which is another reason to add the additional 20 percent load to your calculations as I recommended.

Fortunately, as UPS devices rise in cost, VA ratings rise comparably. For example, the Tripp Lite SmartOnline 6000 RT3UUPS System has a VA rating of 6,000 and can run for up to 24 minutes at half load (3,000 VAs worth of equipment running at full power). So for this UPS, a total of 83 Cobalt RaQ 4 systems could be attached for a full load.

Some UPSs will deliver power to attached equipment that exceeds the UPS’ VA rating while power is actively supplied to the UPS. However, should the active power source fail, the UPS won’t be able to provide more VAs than it’s rated for. Most UPSs cannot provide power above their VA rating at all, though, so it’s wise to always err on the side of caution and make sure your UPS has enough headroom to temporarily exceed the needs of the systems you want to protect.

One final note about load: Laser printers and UPS units are generally not good companions. You should never connect a laser printer to a UPS, because laser printers draw massive amounts of power at unpredictable times.

Maintaining a UPS
Proper maintenance of a UPS is critical for its continuous operation. Just like any server, router, switch, or air-handling unit in a server room, a UPS requires maintenance. There’s always a chance of failure in any man-made device, and if you don’t maintain it properly, that failure can occur at the worst possible moment.

Prevent downtime during maintenance
Just like these other devices, a maintenance contract will guarantee that the unit will be repaired within a certain time frame should they fail. With a properly designed power distribution system, minor UPS downtime for repair and maintenance will not result in equipment downtime. Many organizations implement a power system backed by multiple UPS units, each of which is capable of handling the entire load for their infrastructure. Depending on how critical the environment is, this ensures that at least one UPS will be able to assume the load in the event of a failure.

UPS periodic maintenance can be done without having to involve a repair company. Naturally, you don’t want to do run maintenance on a UPS at a time when users are working on the test network. It’s best to do this after tasks such as backup jobs are complete and when there are no users trying to access the resources, just in case the UPS is not properly functioning. You should periodically test the unit by running a clean (and full) shutdown of the equipment to be used on the test UPS; migrate this equipment or use identical, nonproduction equipment to a test network away from the main server room; set up and power on all test equipment (attached to the UPS); and simply flip the power breaker for the test network.

Although you may be tempted to just pull the UPS’ plug from the wall to test it, don’t do it. Most UPS vendors highly discourage this. Many vendors, such as Tripp Lite, warn that the UPS must have a constant grounded connection to work properly. When you pull the plug, you disconnect the UPS’ ground circuit and can damage it.

To run the test, plug the server (or other piece of equipment) into the UPS. Once the equipment is attached and running, throw the breaker to the test network server and start timing. The UPS should manage to keep the machine up for the amount of time indicated in the UPS’ manual. Keep a record of this time, because it's the maximum amount of time the production equipment can be expected to run under that particular power consumption scenario.

One misconception about UPS units is that they should be run down completely every so often to keep the batteries in good shape. This is not the case with most UPSs. Few UPS units have the types of batteries with “memory,” like the batteries used in some cell phones. Most have lead-based batteries similar to those in cars.

The only time I would recommend running a UPS battery down is for testing, and then you should only do so on a test network. You can run a battery down to see how long the unit could power a server (or other piece of equipment) under a full load. To set up such a test, I would first make sure the UPS either has a replaceable battery or is a spare that you can afford to lose, because after the test is complete, the battery should not be trusted to supply sufficient power to the attached equipment.

Also make sure you are testing the UPS with a piece of equipment that has similar (if not exact) ratings as the actual production machines. Do not use the actual production machines for this test, because these machines will require an unclean shutdown as the UPS runs out of power. However, this can be avoided if the UPS uses software to cleanly shut down the machine. Make sure that you duplicate the load the production machines will put on the UPS. If you are attaching three servers to the UPS, each with a VA rating of 72, make sure the test setup is equal in VA rating.

Don't forget the batteries
UPS batteries also need periodic maintenance. In fact, batteries actually need to be replaced every so often because over time, they become less able to hold a charge and will not provide as much uptime in the event of a problem. The frequency with which you must replace batteries varies depending upon the manufacturer. Making battery replacement part of a maintenance contract will ensure that the batteries are replaced on schedule. UPS batteries can last anywhere from one to five years, but it is important to check with the manufacturer for specific guidelines.

Some UPS units, such as the Fenton PowerPal 425VA UPS, support hot swappable batteries, which you can replace without having to shut down either the UPS or the attached equipment. In these units, power is supplied to the connected equipment via a pass-through connection. As a result, if the power goes out in the middle of the battery replacement, the UPS will not be able to assume the load. So you shouldn't replace batteries when your servers are in the middle of important transactions, such as conducting backups, database replication, or file transfers.

Whether the UPS has a hot swappable battery or just a standard replaceable battery, always have at least one extra battery on hand. Even with immaculate maintenance records, it is easy to forget to replace a battery or have a battery go bad.

Learn from my mistakes
To keep your UPS running efficiently and for a long time, you must perform routine maintenance, management, and optimization. Too many times, I’ve neglected a UPS only to have it fail and lose critical data. After my last failed unit, all my UPS devices wound up on my regular maintenance routine. I’ve not suffered data loss from power failure since.

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