Hey all,
 
I've got an Ultra m923 case, like so:
 
http://www.ultraproducts.com/produ [...] ductID=687
 
with a Intel Quad Core 2.4Ghz Q6600 CPU, GTX 9800 graphics card and 6 hard drives.  The case has space for 4x 120mm fans, so I'm wondering what the recommended way to set these up is, there's one on top, one at the rear, and two which you can mount at the front inside the hard drive cages.  I have a huge Thermaltake Golden Orb II Cooler on the CPU so the temp of the CPU is a non-issue, especially since I'm not overclocking it.  I am not often running the latest games on it which would heat up the GTX 9800, so I'm not worried about that either.  However 5 of the hard drives are in a RAID array that gets routinely hammered so I want these properly cooled.
 
What I'm mostly bothered about is that the side panel of the case is vented in two places, the first is right above the CPU fan, the second is away from the CPU in no particularly special place (i.e. there's a grill area... basically holes in the side of the case) but there's no mesh there to stop dust.  So if I stick all 4 fans blowing out, then all the air is going to get sucked in through that vent, including sucking in piles of dust.  The two hard drive cages however do have a mesh in front of them.
 
So what I was thinking of doing was:
1) Setting the top and rear fans to blow out
2) Setting the fans in the hard drive cages to suck in, right into the mesh grills which will hopefully stop a lot of the dust from getting into the case
3) Block up the second of the vents on the side of the case so the air HAS to come in past the mesh grills (I won't block up the vent that's right above the CPU fan... while I've got a huge CPU heatsink/fan I don't want to push my luck)
 
Any thoughts on this would be most appreciated
 
Thanks,
 
Nigel.

Exhaust on top and rear, intake on front and sides.  That's about all you need to know about location.
 
Then there's air pressure!  You generally want to keep negative pressure otherwise too many hot-pockets build up inside the case.  That means you want more exhaust than intake.  A good case will have extra intake vents vs exhaust vents to allow a place for air to come in when exhaust exceeds intake (ideal).  One way to ensure this pattern is to get lower CFM intake fans and higher CFM exhaust fans.  Or if you want you can get variable-speed fans (same brand/type, if you want good lifespan/warranties) and just keep the intake fans slightly lower.  You'll also want to remember that PSU fans are exhaust fans, and if you have a dual-slot video card, that will also exhaust air from your case.
 
An easy way to test what kind of pressure you have is to put a piece of something like a plastic bag or light sheet of paper in front of a vent, and see if it sucks or blows.  Don't put it in front of a fan though cuz you'll obviously get what the fan is doing

Leo,
 
Thanks very much for your quick answer
 
>> Exhaust on top and rear, intake on front and sides.
Right, will do.  Basically what I figured, but I couldn't find anything online confirming that was the right thing to do.
 
>> Then there's air pressure....you want more exhaust than intake
I will have, since the two intake fans on the front have the grills in front of them which will drastically reduce how much air they're sucking in.  I checked, the CPU fan is also sucking in rather than blowing out.
 
Thanks again for your help,
 
Nigel.

And most fans, somewhere on the shroud, have an airflow directional indicator. Also, the side with the label on the center hub is the exhaust side.