Data Center Definition and Solutions

Data Center topics covering definition, objectives, systems and solutions.

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Cogeneration: This is the use of an engine (typically diesel or natural gas based) to generate electricity and useful heat simultaneously. The heat emitted by the engine in a data center application can be used by an "absorption chiller" (a type of chiller that converts heat energy into cooling) providing cooling benefits in addition to electric power. In addition, excess electricity generated by the system can be sold back to the power grid to defray costs. In practice, the effective ROI of cogeneration is heavily dependent on the spread between the cost of electricity and fuel. The cogeneration alternative will also contribute to substantial increase in CO2 emissions for the facility. This runs counter to the trend toward eco-friendly solutions and will create a liability in Cap and Trade carbon trading.

Colocation: Colocation is one of several business models where your data center facilities are provided by another company. In the colocation option, data centers for multiple organizations can be housed in the same facility sharing common power and cooling infrastructure and facilities management. Colocation differs from a dedicated hosting provider in that the client owns its own IT systems and has greater flexibility in what systems and applications reside in their data center. The lines are blurred between the various outsourcing models with variations in rights, responsibilities and risks. For this reason, when evaluating new facilities it is important to make sure the business terms align properly with your long term needs for the space.

Containers: The idea of a data center in a container is that all the power, cooling, space and connectivity can be provisioned incrementally through self contained building blocks, or standard sized shipping containers. These containers can be placed outside your place of business to expand data center capacity or may be deployed in a warehouse type environment. The primary benefit data center containers provide are that they support rapid deployment and are integrated and tuned to support very high power densities. Containers have been embraced for use in cloud type services by Google and Microsoft. The potential downsides of containers are several: They are expensive (more per useable SF than custom built facilities), tend to be homogeneous (designed for specific brands/models of systems) and are intended for autonomous operation (the container must remain sealed to operate within specifications).

CRAC (Computer Room Air Conditioner): A CRAC is a specialized air conditioner for data center applications that can add moisture back into the air to maintain the proper humidity level required by the electronic systems.

DX cooling (direct expansion): A compressor and glycol/refrigerant based system that uses airflow to dissipate heat. The evaporator is in direct contact with the air stream, so the cooling coil of the airside loop is also the evaporator of the refrigeration loop. The term "direct" refers to the position of the evaporator with respect to the airside loop. Because a DX-based system can reduce the air temperature by a maximum of 23° F, they are much more limited in application when compared to more flexible chiller based systems.

Economizer: As part of a data center cooling system, air economizers expel the hot air generated by the servers/devices outdoors and draw in the relatively cooler outside air (instead of cooling and recirculating the hot air from the servers). Depending on the outdoor temperature, the air conditioning chiller can either be partially or completely bypassed, thereby providing what is referred to as free cooling. Naturally, this method of cooling is most effective in cooler climates.

Fan tile: A raised floor data center tile with powered fans that improve airflow in a specific area. Fan tiles are often used to help remediate hot spots. Hot spots are often the result of a haphazard rack and server layout, or an overburdened or inadequate cooling system. The use of fan tiles may alleviate a hot spot for a period of time, but improved airflow and cooling systems that reduce electricity demands generally are a better option for most facilities.

Floor to Ceiling Height: In modern, high-density data centers, the floor to ceiling height has taken on greater importance in site selection. In order to build a modern, efficient facility, best practices now call for a 36-foot (or more) raised floor plenum to distribute cool air efficiently throughout the facility (with overhead power and cabling). In addition, by leveraging the chimney effect and hot air return, the system can efficiently reject the hot air while introducing a constant flow of cool air to the IT systems. To build a facility upgradeable to 400 watts/SF, you should plan on a floor to ceiling height of at least 18 feet. Some data center designs forego a raised floor and utilize custom airflow ducting and vertical isolation. Since this is a fairly labor intensive process and is tuned to a specific rack layout, it may not be suitable for installations where the floor plan is likely to evolve over the life of the data center.

Flywheel UPS system: A low-friction spinning cylinder that generates power from kinetic energy, and continues to spin when grid power is interrupted. The flywheel provides ride-through electricity to keep servers online until the generators can start up and begin providing power. Flywheels are gaining attention as an eco-friendly and space saving alternative to traditional battery based UPS systems. The downside to flywheel power backup is that the reserve power lasts only 15-45 seconds as compared to a 20 minute window often built into battery backups.

Hot Aisle/Cold Aisle: Mixing hot air (from servers) and cold air (from air conditioning) is one of the biggest contributors to inefficiencies in the data center. It creates hot spots, inconsistent cooling and unnecessary wear and tear on the cooling equipment. A best practice to minimize air mixing is to align the racks so that all equipment exhausts in the same direction. This is achieved simply by designating the aisles between racks as either exclusively hot-air outlets or exclusively cool-air intakes. With this type of deployment, cold air is fed to the front of the racks by the raised floor and then exhausted from the hot aisles overhead.

NOC (Network Operations Center): A service responsible for monitoring a computer network for conditions that may require special attention to avoid a negative impact on performance. Services may include emergency support to remediate Denial-of-Service attacks, loss of connectivity, security issues, etc.

Rack Unit: A rack unit or U (less commonly, RU) is a unit of measure describing the height of equipment intended for mounting in a computer equipment mounting rack. One rack unit is 1.75 inches (44.45 mm) high.

RTU (Rooftop Unit): RTUs allow facilities operators to place data center air conditioning components on the building's roof, thereby conserving raised white space while improving efficiency. In addition, as higher performance systems become available, RTUs can be easily upgraded without affecting IT operations.

Power-density: As servers and storage systems evolve to become ever more powerful and compact, they place a greater strain on the facility to deliver more power, reject more heat and maintain adequate backup power reserves (both battery backup and onsite power generation). When analyzing power-density, it is best to think in terms of Kw/rack and total power, not just watts per square foot (which is a measure of facility capacity). Note: See watts per square foot.

Power Density Paradox: Organizations with limited data center space often turn to denser equipment to make better use of the space available to them. However, due to the need for additional power, cooling and backup to drive and maintain this denser equipment, an inversion point is reached where the total need for data center space increases rather than falls. This is the power density paradox. The challenge is to balance the density of servers and other equipment with the availability of power, cooling and space in order to gain operating efficiencies and lower net costs.

Raised-floor plenum: This is the area between the data center sub floor and the raised floor tiles. It is typically used to channel pressurized cold air up through floor panels to cool equipment. It has also been used to route network and power cables, but this is not generally recommended for new data center design.

Remote hands: In a hosted or colocation data center environment, remote hands refers to the vendor-supplied, on-site support services for engineering assistance, including the power cycling of IT equipment, visual inspection, cabling and maybe even swap out of systems.

Steam Humidification: Through the natural cooling process of air conditioning, the humidity levels of a data center are reduced, just as you would find in a home or office air conditioning environment. However, due to the constant load of these AC systems, too much moisture is removed from most IT environments and must be reintroduced to maintain proper operating humidity levels for IT equipment. Most CRAC units use a relatively expensive heat/steam generation process to increase humidity. These steam-based systems also increase the outflow temperature from the CRAC unit and decrease its overall cooling effectiveness. See: Ultrasonic humidification

Ultrasonic Humidification: Ultrasonic humidification uses a metal diaphragm vibrating at ultrasonic frequencies and a water source to introduce humidity into the air. Because it does not use heat and steam to create humidity, ultrasonic systems are 95% more energy efficient than the traditional steam-based systems found in most CRAC units. Most environments can easily be converted from steam based to ultrasonic humidification.

UPS (Uninterruptible Power Supply): This is a system that provides backup electricity to IT systems in the event of a power failure until the backup power supply can kick in. UPS systems are traditionally battery and inverter based systems, with some installations taking advantage of flywheel-based technology.

VFD (Variable Frequency Drive): A system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. VFDs save energy by allowing the volume of fluid/air to adjust to match system's demands rather than having the motor operating at full capacity only.

Virtualization: As servers have become more and more powerful, they have also (in general) become underutilized. The challenge to IT organizations has been to compartmentalize applications so they can be self contained and autonomous while at the same time sharing compute capacity with other applications on the same device. This is the challenge addressed by virtualization. Virtualization is the creation of a virtual (rather than actual) version of something, such as an operating system, a server, a storage device or network resources. Through virtualization, multiple resources can reside on a single device (thereby addressing the problem of underutilization) and many systems can be managed on an enterprise-wide basis.

Watts per Square Foot: When describing a data center's capacity, watts per square foot is one way to describe the facility's aggregate capacity. For example, a 1,000 square foot facility with 1 MW power and cooling capacity will support an average deployment of 100 watts per square foot across its raised floor. Since some of this space may have CRAC units and hallways, the effective power density supported by the facility may be much greater (up to the 1MW total capacity). Facilities designed for 60 W/SF deployments just a few years ago cannot be upgraded to support the 400 W/SF loads demanded by modern, high density servers. Note: See power-density.

Michael Bullock is the founder and CEO of Transitional Data Services (TDS), a Boston, MA-based consulting firm focusing on green data centers, data center consolidation / relocation, enterprise applications and technical operations. Prior to founding TDS, Bullock held executive leadership positions at Student Advantage, CMGI and Renaissance Worldwide.


Copyright © 2009 IDG Communications, Inc.

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