Raised floors were once a standard feature of data centers, but over time a steadily growing fraction of data centers are built on hard floors. Many of the traditional reasons for the raised floor no longer exist, and some of the costs and limitations that a raised floor creates are avoidable by using hard-floor designs. This paper discusses factors to consider when determining whether a data center should use a raised floor or a hard floor design.
Many of the reasons that led to the development of the raised floor no longer apply. The absence of a compelling requirement for a raised floor combined with the cost and limitations of a raised floor in supplying energy efficient cooling to high density data centers, suggests that many new data centers should consider designs based on a hard-floor. Hard floor designs are now routinely implemented in all kinds of data centers, and are the dominant form in server rooms and hyperscale data centers. Our experience shows that data center operators do not tend to return to raised floors after they have built a hard floor data center. Nevertheless, data centers are likely to use raised floors for some time due to a large base of experience with raised floor design, traditions of locating piping and wiring under the floor, and the intangible issues of perception and image. Data centers that have existing raised floors often have difficulty supplying sufficient airflow to newer high density IT loads due to underfloor cable congestion and low plenum height, resulting in energy inefficiency and hot-spots. While moving cabling overhead in such situations can improve this condition, cooling solutions such as row-based cooling, hot aisle containment, and cold aisle containment can be applied to high-density pods to reduce the underfloor airflow requirement and extend the data center life.