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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?"
Where else am I going to store my beer so it can stay cold and the boss not find it?
But then where will we keep the bodies?
As long as the space under the floor has a negative or positive atmosphere I can't see how somme turns have anything to do with the air flow.
I thought the raised flooring was just to make the people working there look taller and more impressive, kinda like how they do with pharmacists.
Another big reason for raised floors is to handle wiring. I know companies where it was installed only for this reason. Cooling wasn't even on their minds.
Proverbs 21:19
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!
To paraphrase a popular saying: "It's the COMPUTERS, stupid!"
Inefficient architectures must be discarded to make way for more modern, smaller, COOLER processors.
Let's address the real problem here -- not the SYMPTOM of hot air.
We need to address the COMPUTERS.
If you "get" pointers add me as a friend (116)!
Just have the whole data center submerged in an inert solution like the one made by 3M (fluorinert?), and have the workers wear scuba equipment.
Most. Efficient. Cooling. Evar!
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...)
But it also eliminates the joy of making fun of coworkers who gets lost in a raised floor, or closing them in when they go on a hunt for something...
(S(SKK)(SKK))(S(SKK)(SKK))
So long as you have positive air pressure under your floor, you'll get *some* effect from your perf tiles. However, as I'm sure some fluid dynamics folks will jump in with, air flow is a HARD problem. Yeah, so you're getting cold air coming up through your perfs. Well, most of them. Some of them are actually pulling air DOWN. Why?
:)
If you're bored, check out TileFlow. It's an underfloor airflow simulator. You put in your AC units, perf tiles, floor height, baffles, you name it. It will (roughly) work out how many CFM of cold air you're going to see on a given tile. It's near-realtime (takes a second to recalculate when you make changes), so you can quickly add/remove things and see the effect. I spent some time messing with this a couple of years ago, and it's very easy to set up a situation where you have areas in your underfloow with *negative* pressure.
The article basically summed it up for me:
McFarlane said raised floors should be at least 18 inches high, and preferably 24 to 30 inches, to hold the necessary cable bundles without impeding the high volumes of air flow. But he also said those levels aren't realistic for buildings that weren't designed with that extra height.
I'd go with 24 inches MINIMUM, myself. Also, proper cable placement (ie: not just willy-nilly) goes a long way towards helping airflow issues. Like they said though, you don't always have the space.
Of course, with the introduction of a blade chassis or 4, you suddenly need one HELL of a lot more AC
Endless arguments over trivial contradictions in books written by ignorant savages to explain thunder in the dark.
That only works until you have a situation where you need to cut the green wire with the yellow stripe, NOT the black wire with the white stripe, in order to shut down your server before it explodes. That oxygenated fluid is pink, making colour detection damn near impossible.
Now, if you're willing to host an alien spaceship at the bottom of your datacentre, maybe they could lend a hand...
Endless arguments over trivial contradictions in books written by ignorant savages to explain thunder in the dark.
Raised flooring is useful for several reasons, moving cool air through a data center is only one of them. While requiring air to make severe turns to get out of the floor isn't optimal, most cabinets and the equipment in those cabinets is engineered with this in mind. Air is generally drawn in through the front of the cabinet and device and warm air blows out the back. Fans in the equipment pull the air in - the air doesn't have to "turn" on its own again (not that is really did in the first place). Warm air then rises after leaving the device where it is normally drawn back into the top of the AC unit.
Raised flooring also provides significant storage for those large eletrical "whips" where 30A (in most US DCs any how) circuits are terminated as well as a place to hide miles of copper and fiber cable (preferably not too close to the electrical whips). Where else would you put this stuff? With high density switches and servers, we certainly aren't seeing less cable needed in the data centers. Cabinets that used to hold five or six servers now hold 40 or more. Each of these needs power (typically redundant) and network connectivity (again, typically redundant), so we actually have more cables to hide than ever before.
Cabinets are built with raised flooring in mind. Manufactureres expect your cabling will probably feed up through the floor into the bottom of the cabinet. Sure, there is some space in the top of the cabinets, but nothing like the wide open bottom!
Anyhow, there you have the ideas of someone who is quickly becoming a dinosaur (again) in the industry.
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.