Server Density Makes Your UPS More Critical Than Ever

By Drew Robb (Send Email)
Posted Jun 13, 2007


Shifts in power densities brought on by blades and multi-core processors is also bringing change to the uninterruptible power supply (UPS) market. System architectures have had to become more flexible in order to provide greater amounts of standby power, and also to be able to place additional UPS units within the racks themselves.

As blade servers and multi-core processors become more prevalent in the server room, the role of uninterruptible power supplies is changing and becoming even more important.

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"Today's data centers were not designed for racks of blades," said Greg Palmer, product line manager for APC-MGE of West Kingston, R.I.

As a result, the UPS marketplace has broadened to take into account a wider set of customer needs and environments. The resulting products range from simple offline units for individual servers to online (also known as double conversion) systems that can either be placed outside the server room, at its edge or within the rack itself.

The UPS Lineup of Players
Liebert Corp, of Columbus, Ohio, for example, offers several UPS lines. The Liebert Series 610 is aimed at large data centers. It includes several new features designed to enhance performance, efficiency, application flexibility and reliability. It spans from 100kVA to 1MVA with prices ranging from $30,000 to $130,000.

Liebert Npower UPS range from 30kVA to 130kVA with prices from $17,000 to $35,000. Its target markets are server rooms, data processing, medical imaging equipment, industrial process equipment and laboratories.

"This medium-sized UPS has double-conversion online technology that protects against the full spectrum of input and output power disturbances," said Peter Panfil, vice president of power engineering at Liebert. "It can make ultra-fast adjustments to changing loads."

For smaller environments that require up to 30 kVA, the Liebert NX is a double conversion digital UPS. It incorporates power factor correction. Pricing starts at $8,442.

Liebert also offers an alternative to the traditional power distribution architecture. Normally, the utility input is fed into the UPS system and from there to centralized power distribution units (PDU) and then into the equipment racks. Instead, the company advocates a two-stage design with two UPS systems with two stages of PDU's in order to bring the power much closer to the racks. This is designed gto enable better power management, more efficiency and lower costs.

Rittal GmbH & Co. of Germany is best-known as a maker of racks. But it augments this business with modular UPS units that can be placed within or beside the racks. Its PMC 2000 is available in modules that range from 8kW up to 40 kW. That enables a fine graduation of power levels that can be added to easily in order to prevent overbuying.

"These units are up to 96 percent efficient," said Jörg Kreiling, product manager for IT solutions at Rittal. "It is a double conversion UPS and more modules can be added or swapped out during operation."

Smaller server rooms may want to consider the Pulsar MX UPS by MGE Office Protection Systems, (O.P.) Systems of Costa Mesa, CA. It fits into the 5 to 20 kVA range and costs anywhere from $ 3,936 to 14,236 depending on the size and configuration.

"The Pulsar MX protects 20 to 110 servers," said Brad Amano, business development manager for MGE OP Systems. "When connected in parallel within the Pulsar Frame modular chassis, the Pulsar MX sub-modules can be readily scaled to 10, 15 or 20kVA power levels."

When it comes to more substantial needs, however, APC-MGE's Symmetra line provides the capability to scale power and runtime, as well as fault tolerance.

"Larger companies running with critical applications and devices may require a higher degree of reliability," Palmer said. "For these users, which typically have a larger multiple rack mounted servers with converged voice/data networks, Symmetra offers a good solution."

The Symmetra PX, for example, provides 160 kW of UPS. According to Palmer, it has double the power, longer battery life and up to 25 percent more runtime compared to the previous generation. As it has an integrated battery, bypass and distribution cabinet design, it is also smaller than its predecessor.

Sizing and Maintenance
Many companies don't realize that a UPS can be the deciding factor in how many blades can be crammed into a facility. At the data center of Danfoss A/S in Denmark, server room density is inhibited by UPS. The facility currently has a large UPS room in the basement, but this only has a capacity of 160 kW.

"We have had to leave older rack servers in place rather than import more blades as we are currently at our UPS limit," said Jan Petersen, IT production manager at Danfoss. "We are looking at adding an APC Symmetra UPS in order to upgrade our older racks."

To prevent such situations, UPS vendors suggest that companies total up the number of kW consumed by existing devices and then adding a safety factor of 10 to 20 percent. Enterprise should also calculate the amount of battery runtime required. Most systems need only five to ten minutes to power down. But some facilities may want more for mission-critical hardware.

"Correctly dimensioned UPS systems save costs and at the same time increase the availability of data centers," said Kreiling.

As a rule of thumb, older racks are in the 1 to 3 kW range, most modern racks range from 3 to 10 kW, and densely packed blades can be anywhere from 10 to 30 kW.

As well as correct sizing, server administrators need to pay attention to UPS maintenance. In particular, batteries need attention. Typically, these are sealed lead acid batteries with a life expectancy of three to five years.

Longevity depends upon the amount of battery usage and factors such as temperature. In the event of a blackout, server UPSs fully loaded can provide five to ten minutes. In practice, however, most are not fully loaded and provide longer runtime. Thus, if UPSs don't have to run often, aren't fully loaded (ideally, keep them below 80 percent load) and aren't used for their maximum runtime each time, they will last longer.

In addition, Palmer of APC-MGE offers some maintenance tips: The UPS unit should be kept in a cool, dry location with plenty of ventilation around the box. Battery life is longer when temperatures are kept below 75 degrees F. Another tip concerns runtime calculations. Some server admins perform these regularly. Palmer cautions that doing so can decrease battery life. He suggests runtime calculations be done only once or twice per year. Finally, he said don't store batteries for long periods.

"New batteries can be stored for six to 12 months," Palmer said. "After this period, the battery should be used or it will lose a great deal of its charge. It is not advisable to store batteries that have already been in use."

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