March 2009 - Tech & Trends
Today, many data centers use raised floors to carry cables, electrical wiring, and cooling equipment. However, more data centers are being built without them. Why is the industry turning away from this concept? And, is this a trend or a fad? Here, we’ll discuss the advantages and disadvantages of using raised floors in the data center and tell you why some data centers are seeking other design concepts.
Going Down
Steve Hambruch, data center architect at Data Center Resources (www.datacenterresources.com), says while raised floors have been the mainstay in data centers for a few decades, their use is declining in new data center build-outs. He explains, “This decline is mainly due to the maturation of the rackmount server as the de facto standard computing platform. Power densities associated with blade servers and high-density server racks have pushed the raised floor plenum to the edge of its capabilities in many data centers. The overuse of the raised floor as a cable-management device has also limited its cooling effectiveness.”
Hambruch says data center managers who are engaging in significant renovations of existing facilities or designing new green field facilities are realizing that greater efficiency and optimization can sometimes be obtained by abandoning perimeter-based, room-level cooling in favor of localized cooling at the row level. He adds, “This approach, often accompanied by hot-aisle or cold-aisle containment, offers significantly increased cooling efficiency in many environments and also more optimal cable management through overhead cable-management devices. However, these performance or efficiency gains are not universally applicable to all designs.”
Steve Yellen, vice president of product and market strategy at Aperture (www.aperture.com), says we are hearing more about the raised floor issue for two reasons: cost and cooling. Yellen comments, “Raised floors can be more expensive. Of course, that always has been the case, but raised floors became the preferred approach because they facilitated the delivery of cool air throughout the data center. But high-density IT environments require even more cooling, forcing data center and IT managers to move to precision cooling in the row or in the rack. If the raised floor isn’t used for delivering cool air, it isn’t necessary.”
In or Out?
Will raised floors eventually disappear? According to Hambruch, they’re not going away anytime soon; he says the move to other solutions is a trend. He notes, “Data center managers and designers have begun to migrate from the ‘that is how we have always done it’ mentality and started looking at innovative alternatives to the typical perimeter-cooled raised-floor environment. I think this trend has resulted from an increased focus on energy costs, ROI, and PUE (power usage effectiveness) industry-wide. Having said that, there are still plenty of environments where traditional raised floor installations are still the most effective solution.”
Robert Neave, CTO of GDCM (Global DataCenter Management; www.gdcm.com), says that this is not a new trend, either. “This trend is one more solution in the increasing toolbox for data center designers; the data center design space is continually evolving as equipment requirements change in these complex environments, and designers are under increased pressures to find solutions that will meet business demands for the life of the data center,” he says.
Pros & Cons
Can data centers expect to save costs by removing raised floors? Neave says yes and no. “Some designers will argue,” he says, “that by removing the plenum, you eliminate the expense of heavy plant equipment to cool the data center and the costs of under-floor maintenance, while other designers will argue that you have just moved the maintenance pains and cost to above the floor or rack.” Neave says the cost savings for data center design are a difficult juggling act of what is “in” and “out” of scope and is always limited by the capacity information provided at design time.
In Yellen’s opinion, you can definitely save costs in new data centers, but there really aren’t any significant savings to be achieved by transitioning from raised floor to slab in an existing facility. He says the decision to redesign a data center and switch from raised floor to slab would have more to do with maximizing available space. In terms of the easiest solution for running cables, Yellen says that is largely a personal preference. He notes, “I know some data center managers believe that cables mounted along the ceiling are more accessible. Others believe the inconvenience of using a step ladder makes under-floor cabling a better choice.”
Hambruch, on the other hand, says under-floor cable management hinders cooling effectiveness for the critical equipment. Also, under-floor cable management tends to invite greater cable abandonment issues over time. The cabling falls into the “out of sight, out of mind” trap. Overhead cable management typically presents less of a disruption to the delivery of cooled air to the critical equipment, and the visibility of the cabling system aids in identifying and rectifying cable-management challenges, such as cable abandonment.
The key advantages to not using a raised floor, Yellen says, are the lower cost of construction and more available space. “A slab is more stable,” Yellen says, “which is important in locations prone to earthquakes, and also easier to keep clean and relatively dust-free. In terms of disadvantages, the common concern is accessibility of cables mounted overhead and the inconvenience of using a step ladder.”
Neave says there are advantages and disadvantages to both approaches. He elaborates, “Very few data centers we build from the ground up are standard rooms that have been repurposed for data center support. If these rooms have high ceilings, it can be very expensive to get the overhead cooling close enough to the tops of the cabinets to effectively cool the equipment. In these cases, a raised floor approach might be the better choice. The raised floor can be a very expensive proposition in large data centers.”
Hambruch concludes, “It is generally not as effective for rooms that support heterogeneous platforms including large storage appliances, mainframe equipment, and other equipment that is designed to work in a raised floor environment.”
