I hang my hard drives from a strip of 1/8" plywood. I think I space the holes 1-1/8" apart. That gives a 1/8" (3mm) gap between drives. I have my fans pushing air into the spaces (4 4" fans for 8 drives works well for me).
I don't think the air flow direction matters as much as having the fans near the hard drives. My fans are 1/2" away from the hard drives.
Sorry for reviving an old thead but this is exactly what I'm looking for!
I've run out of room in my server and am wondering if you could provide some info on the metal/method you used to make those rails (and also how it's been working for you since doing it!)
Any additional info you can provide would be great
Sounds ghetto but you can use pipe strap as well. I drilled out the rivets from an old case, cut pipe strap and bent it to how I wanted it, used a rivet gun to install the pipe strap and it's been solid since. Only vibration issues I have is the case on the solid surface...which rubber feet take care of - green drives seem to spin slow enough to not cause problems.