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Raised Flooring Obsolete or Not?
mstansberry writes "In part three of a series on the price of power in the data center, experts debate the merits of raised flooring. It's been around for years, but the original raised floors weren't designed to handle the air flow people are trying to get out them today. Some say it isn't practical to expect air to make several ninety-degree turns and actually get to where it's supposed to go. Is cooling with raised floors the most efficient option?"
I interned at ARL inside of Aberdeen Proving Grounds this past summer and when touring the supercomputer room (more like cluster room these days), the guide said they used one of the computers in the room to simulate the airflow in that room so they could align the systems for better cooling. How geeky is that!
Indeed. It's been years since I've seen a raised floor. As far as I know, most new datacenters use racks and overhead wire guides instead. The reason for this is obviously not the air flow. The raised floor made sense when you had only a few big machines that ran an ungodly number of cables to various points in the building. (At a whopping 19.2K, I'll have you know!) Using a raised floor allowed you to simply walk *over* the cabling while still allowing you to yank some tiles for easy troubleshooting.
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:-)
(Great way to keep your boss at bay, too. "Don't come in here! We've got tiles up and you may fall in a hole! thenthegruewilleastyouandnoonewillnoticebwhahaha"
With computers being designed as they are now, the raised floor no longer makes sense. For one, all your plugs tend to go to the same place. i.e. Your power cords go to the power mains in one direction, your network cables go to the switch (and ultimately the patch panel) in another, and your KVM console is built into the rack itself. With the number of computers being managed, you'd be spending all day pulling up floor tiling and crawling around in tight spaces trying to find the right cable! With guided cables, you simply unhook the cable and drag it out. (Or for new cables, you simply loop a them through the guides.)
So in sort, times change and so do the datacenters.
Javascript + Nintendo DSi = DSiCade
you're right in some sense, the pressure underneath the
plenum will force air through no matter what. there
are however two problems. the first is that turbulence
underneath the floor can turn the directed kinetic energy
of the air into heat...this can be a real drag. in circumstances
where you need to move alot of air, the channel may not
even be sufficiently wide.
more importantly, the air ends up coming out where the
resistance is less, leading to uneven distribution of
air. if you're grossly overbudget and just relying on
the ambient temperature of the machine room, this isn't
a problem. but when you get close to the edge it can
totally push you over.
Someone needs to create an air interconnect standard that lets server room designers snap-on cold air supplies onto a standard "air-port" on the box or blade. The port standard would include several sizes to accomodate different airflow needs and distribution form large supply ports to a rack of small ports on servers. A Lego-like portfolio of snap-together port connections, tees, joints, ducts, plenums, etc. would let an IT HVAC guy quickly distribute cold air from a floor, wall or ceiling air supply to a rack of servers.
Two wrongs don't make a right, but three lefts do.
If something is airtight, putting air in one end will move air out the other end.
The problem lies with larger datacenter environments. Imagine a room the size of a football field. Along the walls are rows of air conditioners that blow cold air underneath the raised floor. Put a cabinet in the middle of the room and replace the tiles around it with perforated ones and you get a lot of cooling for that cabinet. Now start adding more rows & rows of cabinets along with perforated tiles in front of each of them. Eventually you get to a point where very little cold air makes it to those servers in the middle of the room because it's flowing up through other vents before it can get there. What's the solution? Removing servers in the middle of hotspots & adding more AC? Adding ducting under the floor to direct more air to those hotspots? Not very cheap & effective approaches...
it can turn on a dime, but also stay on that dime. poor circulation results. trumpets have nice (if tight) curves, and even building ducts can have redirects inside the otherwise rectangular ducts to minimize trapped airflow in corners. for the most part even those corners are curved to help the stream of air.
most server rooms aren't part of the duct, for example, the one here is large and rectangular, with enormous vents at either end. not very well designed.
airflow is a very complicated problem, my old employer had at least three AC engineers on full time staff to work out how to keep the tents cold ( I worked for a circus, hence the nick.) the ducting we had to do in many cases was ridiculous.
why do you think the apple engineering used to use a cray to work out the air passage through the old macs. just dropping air-conditioning into a hot room isn't going to do jack if the airflow isn't properly designed and tuned. air, like many things, doesn't like to turn 90 degrees, it needs to be steered.
-- it's ridiculous how many people misspell ridiculous... (damn, damn, damn...)
Obviously you realize that as the equipment contents of datacenters change, it doesn't make sense to change the room sturcture all that much? Hence many older datacenters have retained their raised floors. Of course, their air conditioners were also designed for raised floors.
... hence, they still routed cables under the floor for them, by design.
I don't know where you've worked, but every datacenter I've seen has had a raised floor, and all of them still had at least one mainframe structure still in use
[You have a stable society when some nut guns down a schoolyard and the law doesn't change.]
There are a number of slashdot visitors that do actually care about server room issues. The fact that you don't understand the need does not negate it's importance.
Large organizations rely on server rooms for their computing environment. Having a cobbled environment where the file server is on the 3rd floor, and the application server is in the janitor's closet, etc. is a recipe for disaster. Troubleshooting connectivity issues (among others) can end up costing more than the apparent simplicity of such a design.
Understanding ways to better cool the space that our servers occupy is important. And being able to do so in a cost effective manner is also important. The organization that I work in has one in-house server room (containing 60 racks of servers), and one 'co-located' server room (containing 72 racks of servers). Heat and power are the two killers. If we experience a 50% power loss (assume that one power grid is knocked out), do we have enough power to run AND cool the server room? If not, what percentage of my gear do I need to shut down in order to prevent overheating, without impacting critical business systems (like payroll).
If we can find a cheaper / better / more cost effective method for cooling that utilizes less power, or find a way to use the cooling systems that we have in a more efficient manner, is that not worth an article on slashdot?
IMHO, This is a valid topic.
Raised floor cooling was designed back when the computer room held mainframe and telephone switch equipment with vertical boards in 5-7 foot tall cabinets. The tile was holed or removed directly under each cabinet, so cool air flowed up, past the boards and out through the top of the cabinet. It then wandered its way across the ceiling to the air conditioners' intakes and the cycle repeated.
Telecom switching equipment still uses vertically mounted boards for the most part and still expects to intake air from the bottom and exhaust it out the top. Have any AT&T/Lucent/Avaya equipment in your computer room? Go look.
Now look at your rack mount computer case. Doesn't matter which one. Does it suck air in at the bottom and exhaust it out at the top? No. No, it doesn't. Most suck air in the front and exhaust it out the back. Some suck it in one side and exhaust it out the other. The bottom is a solid slab of metal which obstructs 100% of any airflow directed at it.
Gee, how's that going to work?
Well, the answer is: with some hacks. Now the holed tiles are in front of the cabinet instead of under it. But wait, that basically defeats the purpose of using the raised floor to move air in the first place. Worse, that mild draft of cold air competes with the rampaging hot air blown out of the next row of cabinets. So, for the most part your machines get to suck someone elses hot air!
So what's the solution? A hot aisle / cold aisle approach. Duct cold air overhead to the even-numbered aisles. Have the front of the machines face that cold aisle in the cabinets to either side. Duct the hot air back from the odd-numbered aisles to the air conditioners. Doesn't matter that the hot aisles are 10-15 degrees hotter than the cold aisles because air from the hot aisles doesn't enter the machines.
Moderating "-1, Disagree" is simple censorship. Have the guts to post your opinion.