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Tuesday, November 13, 2007

Hot Air

The Problem

At a former company, whose directors were notorious for spending pounds to save pennies, there was a Server Room. It was basically a small room created by partitioning off one part of the developers' room. It had a door, a window, and was quite spacious - more than enough room for the three racks, PBX set up and miscellaneous collection of "Frankenstein" servers (converted desktops) which had been acquired over the years. There was air-conditioning, of course: supplied by a contraption made in Iran, of all places. (Apparently it was very cheap).

Now, this air-conditioning unit had the unfortunate habit of occasionally breaking down when it got too hot, as it tends to in summer. Usually the hardware / admin guy dealt with this: he had a mobile phone connected up to some monitoring system which warned him when certain key servers started going down, as they do when the temperature in the server room breaks through the 50°C barrier. As Murphy would have it, one day I was the only technical person on site, and just as I was getting into the swing of things for the afternoon, my concentration was cruelly intruded upon by loud bleeping noises emanating from the server room. A quick look confirmed my worst fears: the air-conditioning unit's panel lights were blinking a message of woe, and as the thermometer surged past 40°C, the usual hardware foo (check the fuses, switch off and restart etc.) was of no use. Urgent phone calls were made and it was established the air-conditioning guy would come as soon as he could, which would be the early evening if traffic allowed.

(It goes without saying that the air-conditioning guy was a one-man setup: but apparently he was very cheap).

Until then there was the slight problem of keeping the most essential servers from overheating and throwing the company's business offline.

The Solution

First priority was of course to switch off all the non-essential servers (about half), although it was the essential ones which used the most juice. Then it was a question of keeping the room as cool as possible and hoping: the "traditional" method was to gather up all available ventilation fans and put them in front of the most-needy servers while keeping the server room door open. This was better than nothing, but it was a very hot day and to be honest, it wasn't making much difference, especially as the room had one fundamental flaw: the only ventilation possibility was the door itself. The window I mentioned was set in the internal partition wall and couldn't be opened. And without active ventilation the server room was doomed to become a sauna

Standing there working out whether it would be feasible to cart the most critical of the critical servers out into the office and run them there, it occurred to me why the ventilators weren't being much use: all they were doing was circulating the hot air trapped in the server room over the servers, and if anything contributing to the negative feedback loop. What was needed was cool air from the outside, and a way of getting the hot air out of the room.

I quickly discovered that by placing a couple of ventilators on the floor just outside the server room door, and placing a couple more on top of the server racks so they were blowing outwards towards the door, I could create a rudimentary convection system, with cooler air being assisted in from the outside at floor level and the hotter air being encouraged to circulate back out at the top. It was surprisingly effective - you could actually feel the boundary between the two layers of air as they passed through the doorway and kept the temperature down to a manageable 38°C or so (only 10°C or so more than the ambient temperature in the non-airconditioned offices). It held long enough until the air-conditioning guy finally turned up at about 7pm.

Posted at 6:23 PM |Comments (0)