I never used to worry much about hard drive cooling, my drives barely got warm so why bother? Well that philosophy worked ok, up until higher RPM IDE drives started hitting the market. SCSI HDD owners have known for years about the burden of HDD heat as SCSI drives generally spin faster than the IDE variants of the same era, but IDE HDD owners have been blissfully oblivious to the heat a few extra thousand RPM can bring. Test
So it was with some surprise that I discovered my newly purchased IBM 20 Gb 7,200rpm IDE drives (running in a RAID 0 array) where getting quite quite toasty sitting in the bog standard HDD rack. Suddenly I was faced with a new cooling challenge! I looked at some of the HDD coolers available, most were pretty lame and only blew air on on side of the drive and didn't do much to actually get the air out of the case. Even the GlobalWIN ISTORM II, rated as one of the best coolers seems a bit wimpish, especially for the $70 they were asking for it when I devised this plan (no offence to any ISTORM owners, I'm sure your ISTORMS are very mannish).
It makes sense that the best way to air cool a HDD is to blow air all around it, and remove that air from the case so that it doesn't contribute to the cases overall temperature. This meant whatever fan I used had to suck air from the case, pass it over the HDDs and out of the case. If I left the drives in the HDD rack, I would be sucking air from right next to the CPU, thus robbing the CPU of any cool air I was blowing onto it from other fans. The only other spot that could possible house two hard drives and a fan was the bottom from of the case... so that was that then.
Next
came a plan so cunning, it was developed by a Professor C. Fox at Harvard's
Department of Cunningness. I already knew that one could find plenty of ducting
material in PVC plumbing supplies, but most of that stuff is round. Hard drives
are not. Eventually I found the right combination of bits to make a duct
containing the HDDs complete from fan to room.
The pic on the right shows the 100x50mm tin down piping used to
house the HDDs themselves. This is pretty simple to make, just cut to length,
measure the right spots for the screws and drill some holes. The tricky part is
the routing of the IDE cables. As you can see, I used some rubber grommets I got
from my local Autobarn You still have to do some 
manipulation
to get the cable through, I really should have rounded them first, but I wasn't
sure about rounding ata66 cables and I don't have any spares yet in case I screw
it.
Next come the 100x50mm to 80mm collar PVC bits. One vents to the atmosphere and the other connects to the fan. Unfortunately, the fan is mounted on a 100mm floor flange (now I can speak fluent plumber speak I'm pretty cool) so I need an 80mm to 100mm converter. Even so, the converter made the overall length of the duct too long so I had to trim all the piping down to the bare minimum length needed to join it all up, and even so I had to pad out the last join with electrical tape to make it fit tight. Basically you can expect to have to fiddle for a while until you get a plan that works, unless your local plumbing supplier has every piece of PVC connector known to man, then you might get lucky ;-)
Now
I had to get the thing to sit up off the base of the case, in line with the
exhaust hole I had cut in my front bezel. I initially propped it up on spare
foam blocks, but this didn't allow me shift the case around much as it would all
tumble about (bad mm-kay). I eventually hit on the idea of securing on the the
PVC pieces to the front of the case using a bracket made out of aluminium
strips. You can get these aluminium lengths at the hardware store for a few
bucks, I had a 90o one handy so I chopped it up and added some bolts... hey
presto!
Next
the hard drives assembly slots in. In this photo you can clearly see the two drives suspended
in mid duct just waiting to have mega CFM blown over them! In case you're
wondering, the cables go to my PCI RAID controller, not the onboard IDE ports,
that's why they're stretched out in that direction.
In
order to power the two drives way down there, I had to get a length of power
cable and some 4 pin molex connectors. You can get these at most computer or
electronics stores. I chose to make mine just the right length and have the two
plugs for the drives with no excess wire between them. This allows for a much
neater result, but does involved some fiddling and soldering. I ran the power
cable between the front of the case and the plastic front bezel once again,
keeping the airflow inside the case unobstructed. Since taking this photo I have
drilled a small hole in the side of the inner PVC pipe and using a small rubber
grommet, fed the power cord out the side of the duct so it doesn't come out and
around as it does in this pic.
Finally
I whack the fan on and plug it in, sweeeeeeeeet. As per all the fans in my case
at the moment, I can switch between 12 and 7 VDC to keep the noise down when
full power cooling is not required. At 7 VDC it's quiet enough not to bother me at all, but I
know some people are very fussy about fan noise. If you wanted to you could use
an 80mm or 92mm fan in this project and still cool the HDDs ok, but I find for a
long defrag (or frag for that matter) session or any HDD intensive work, the 120mm at full power is
the way to go, the air coming out gets really quite warm at times. Do it, you
know you want to.