Zombies. Everything about them says “dead,” except that they just keep on going. The raised floor has many of the same characteristics: despite all manner of arguments and studies claiming it is no longer necessary in data center design, it is still present in the vast majority of facilities. The technical merits—or lack thereof—of using a raised floor have been considered at length, but what will determine if this long-time defining feature of data centers will live on (perhaps as part of the living dead)?
The Raised Floor Has Inertia
The raised floor was once a staple of the data center. Indeed, according to a Schneider Electric white paper (“Re-examining the Suitability of the Raised Floor for Data Center Applications”), it was so standard that “one common definition of a data center is that it is a computing space with a raised floor.” With decades of design experience backing this approach, a company facing a huge investment in a new facility could easily be forgiven for sticking with the tried-and-true approach, even if pundits and studies suggest otherwise. Uptime Institute data pegs use of raised floors at about 90% of data centers (or, at least, 90% of companies running data centers). For a much maligned design strategy, raised floors still have momentum.
Reasonable arguments still support the use of raised floors in certain cases. For instance, the configurability of overhead air ducts in slab (non-raised-floor) designs tends to be limited, which means that changes in rack arrangements can necessitate time-consuming and expensive changes to the cooling system—changes that are made even more difficult when performed on a live data center. When chilled air is delivered under a raised floor, however, simply rearranging perforated floor tiles is enough to change the cooling distribution. Also, the plenum under a raised floor offers room for cabling that doesn’t require the kind of added labor and infrastructure that overhead cabling calls for—cable racks or baskets, for instance.
Furthermore, raised floors do not exclude the possibility of other cooling methods, such as liquid cooling. The plenum can still provide cabling space, for instance, even if it’s not used to deliver cooling. Alternatively, cabling can be suspended above the racks to enable a less cluttered plenum for better cooling—an approach that the Australian Securities Exchange employed for its data center.
Shifting Momentum: Slab
Even though the vast majority of data centers still use a raised floor, building on a slab may capture the future. According to the Uptime Institute, only about 48% of companies plan to use raised floors—a distinct drop from the 90% currently using them. Arguments in favor of avoiding raised floors focus on several areas; the following are a few.
- Improved cooling. The plenum under a raised floor can be subject to obstructions (particularly cabling) and other inefficiencies that hamper cooling. The general consensus is that a raised-floor design cannot meet the cooling needs of higher-density deployments (perhaps in the range of 8–10 kW per rack and up).
- Load capacity. Although raised floors can be constructed to bear almost any weight, the capacity of the floor may become a concern if the data center grows faster than originally planned or new, heavier equipment is deployed beyond what the company had intended at construction time. Furthermore, seismic activity poses a danger to raised floors beyond what slabs face. Concomitantly, safety is also a concern: an employee who forgets to replace a floor tile, for instance, creates a significant hazard.
- Expense. Simply bolting racks to a concrete floor is cheaper than building a raised floor. On the other hand, a slab design requires overhead cable-management infrastructure and cooling ducts (for air-cooled facilities). Depending on the dimensions of the building and the design strategy, the raised floor may consume too much space.
- Cleaning. The plenum under a raised floor is a dirt and debris trap, but cleaning can be problematic. Furthermore, other problems such as addressing (and even identifying) moisture and breaches in walls plague this approach. Also, since out of sight is out of mind, the temptation to leave unused cabling and other junk in the plenum may be irresistible, particularly in a time-pressed environment, thus exacerbating the problem.
- Security. Not only can a raised floor hide junk, it can also hide security threats, including even access points. This concern is particularly acute in the case of colocation facilities that serve multiple customers.
Reality in the Middle
The arguments against the raised floor are more convincing in some cases than others. To say it another way, not every data center is necessarily better off built on a slab rather than a raised floor. One of the critical considerations is power density: higher-density deployments may simply be unable to achieve the necessary cooling capacity or efficiency using a raised floor. (On the other hand, these implementations may be unable to achieve the necessary capacity with any kind of air-based cooling system.)
For certain data center designs, such as those that must accommodate extensive rearrangement of racks, a raised floor may be the best option. The costs of installing overhead cable-management systems and ductwork—combined with the periodic costs of rearranging that infrastructure—may make a hit to cooling efficiency well worth the price. So, from both a technical and cost standpoint, raised floors are not viable in all cases, but they remain a legitimate option in others.
The Hammer of Efficiency—and the Environment
Assuming the raised floor can be outdone in all cases by slab deployments with regard to energy efficiency, should the costs still be a concern? According to Schneider Electric’s Senior VP of Innovation Neil Rasmussen, “Anyone designing a new data center now with raised-floor cooling is being environmentally irresponsible.” He goes on to say that “the future is hard floor data centers because legacy cooling solutions are inappropriate for today’s high-density environments, and to provision dynamic power variation. Legacy cooling is inefficient, costly and wasteful from a carbon footprint perspective.” The matter of environmental stewardship is a tough one for data centers: they consume growing amounts of power, but they do so to serve growing demand. Furthermore, a little more efficiency is always possible—but it’s not always practical. At some point, a small efficiency improvement is a worthwhile sacrifice for the cost savings and other benefits that result. Finding this balance depends on the circumstances—and some of those circumstances may point to a raised floor, which may or may not be integral to cooling.
The raised-floor debate will drag on. Although the general consensus is that cooling using a standard raised-floor deployment is too inefficient for high-density data centers, legitimate reasons for using a raised floor still exist. Although the Uptime Institute estimates that only 48% of companies plan to use raised floors for future data centers, 48% of companies still plan to use them. That number may fall further over time, but it may settle at some proportion according to the requirements of different facilities. In the meantime, the living dead will still walk (or support) most data centers.