Wednesday, June 4, 2014

Raised floor vs slab , yang mana?

What does every data center (DC) have? If you said “data” or “servers,” well, then you’re technically correct. (Go you!) However, sorry to be the bearer of bad news, but neither of those answers is the one we’re looking for. No, you have to look a little bit lower to find the correct response. We’re talking about a floor.
To be fair, every room has a floor, so this may have been somewhat of an unfair question to ask you. Don’t worry, though, because the important part is that we’ve now got your attention and can talk with you a little bit about the two different types of floors you’ll find in a data center: raised and slab. Which one is better? Good question. Let’s explore.
Who Decided Floors Should Be Raised, Anyways?
A long time ago in an IT world far, far away it was decided that raised floors were ideal for any room containing large amounts of computing hardware, and that was that. The raised floor became so ubiquitous that many data operators and managers consider “raised floor space” synonymous with “data center.” If you’re building a center, you’re building it with a raised floor. That’s just the way it is, because that’s the way it’s always been, and there is therefore no sense in questioning it.
So that’s that, then. It looks like we’ve wrapped this blog post up early, and you can now stop reading and return to your regularly scheduled daily tasks and routines. Thanks for reading.
OK, no, that’s not actually it. As much as we love being efficient – hey, we’re data guys, being efficient workflow is in our blood – that’s hardly a comprehensive look at this great debate. DC needs and goals have changed just a smidgen over the last few decades. Today’s centers have requirements that the old IT gods who once decreed “Let there be floors that are raised” couldn’t have possibly foreseen. In fact, many of the functions of raised flooring are performed not down low but up high. Power and data cabling are often run above the ceilings instead of below the floor these days. Meanwhile, it’s become common for modern cooling solutions to be located either overhead or in in-row AC units.
Technology has also gotten dramatically smaller over the years. The raised “access” floor first became popular because computer hardware required enormous cables and connectors to function. How enormous is enormous? Try an inch or more in diameter for cables up to four inches for connectors. It didn’t help things that manufacturers mass-produced cables in fixed lengths, meaning superfluous lengths of them had to be coiled up. Changes in DC requirements started coming in fast and furious, which meant constant cable changes. Raised floors stepped (no pun intended) in to give center managers an easy way to neatly and safely tuck all of those nasty cables and connectors away.
Eventually, somebody got the bright idea to put cooling systems under those raised spaces. This breakthrough came about only after years of operators bundling up like they were about to trek across Antarctica every time they entered a server room because the entire rooms were kept extremely cold in those days. Then came a time that, once again, changing data requirements meant changing the way things were done.
People and companies needed more data…and then even more data…and then even more data than that…and, well, you get the picture here. Point being, the systems were embiggened and their peripherals were spread farther and farther apart to accommodate the nonstop need for increasing amounts of data storage space. This meant that the DCs themselves got bigger, which in turn meant turning an entire center into the world’s largest walk-in refrigerator became expensive, impractical and inefficient – three things all data center managers hate with a passion.
The solution? Spot cooling from below using underfloor air. This meant that raised floors grew from around six inches on average to about 12 inches. Nobody really had to have uniform underfloor pressures back then, so everyone just made sure that a suitable amount of chilled air was run under the floor. Hardware got all of the cooling it needed, the problem was permanently solved; and everyone lived happily ever after with cabling, connectors and cooling systems hidden out of sight and out of mind.
So Raised Access Floors Pretty Much Solved Everything, Right?
Technically speaking, they fixed the problem, yes. Trouble is, they kind of created a new one. Oh boy.
Here’s a shocker: the world’s data storage and access needs have gone right along their merry little way growing larger and larger. That means more and larger equipment is needed, which means major amounts of airflow needs to be run underneath the flooring to keep all of the hardware running cooler and more efficient than ever. Because – and get ready to be shocked by this – users also want to get their enormous swaths of data faster than ever before.
“OK then,” said data center designers, “We’ll just go ahead and create even higher floor plenums, and that will make for plenty of room for huge quantities of chilled air to blow on through. Problem solved.”
If you’ve been paying attention at all so far, then you’ve already guessed that it of course wasn’t that simple. Pumping all of that air through the space below raised floors meant laser-sharp precision was now necessary when placing air conditioners.  Turbulence can cause the air pressure down under to get all out of sorts, which leads to poor air delivery, defeating the entire point of the whole thing (more efficient chilled air flow, if you recall). Now you’re talking about floor heights up to twice the size (or more) of what they once were when DCs first started pumping cold air through their floor cavities. Eventually you have to worry about the servers sitting atop these raised floors are going to be hitting the ceiling, which is obviously no bueno.
So it seems like the more raised floor we come across, the more problems we see, to paraphrase a popular song. And, of course, it’s not just floor height creep that causes concerns. The very act of running air underneath a floor in a center means likely having to comply with Article 645 of the National Electrical Code. (Yeah, that old crazy thing.) Basically, it necessitates the placement of an emergency shutdown button adjacent to exits. This problem can be sidestepped by simply not using a raised floor and instead running chilled water-containing pipelines behind walls or in floors.
So This Means The Death of Raised Floors in DCs, Right?
Once again, things aren’t exactly cut and dry. Stuffing everything that was once below above instead, as was mentioned earlier in this article, is not the simple solution it may at first appear to be. Lower the ceiling enough to fit everything up there and now you’re talking about the same space issues you’d have with excessively raised floors. Also, modern equipment may not have conveniently located water ports near the ceiling, and using a water-cooling solution means concerns about potential leaks. On top of all that, raised floors are even, unlike the uneven slabs that often lie below them for the purposes of flexing when weight is added. Even raised flooring overcomes this issue and makes it easier to roll hardware around and symmetrically line up cabinet rows.
So raised floors do still have many pros that make them attractive to modern data center designers. They also have their share of cons, though. Come back soon for our next blog post, which will explore the alternative: slab floors.
Image Source: Unitrust


  1. Thanks for your post. You are right that Power and data cabling are often run above the ceilings instead of below the floor these days.

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