[rescue] Deciding how to place machines in a rack.

[Earl Baugh]

Ok, I've parsed all this advise, and am going to place the machines as close
as possible.
I do want to understand one thing a bit better regarding the cooling.....
all of the machines I'll have
in the rack do front-to-back air flow (fans in the front and back which pull
air thru the case front to back)

It seems that the recommendation is to keep the back door off, and either
keep the front door off, or get one
that has a lot of ventilation.    This all makes sense with the front to
back air flow.

But I'm curious about two things.  First, I'm trying to understand the
purpose of the fans at the top of the rack.
If this approach is to move the hot air out the back, I'm thinking I'll just
have a hot spot behind the rack and that the top fans will
just be pulling air from the front and back near the top.   Is this really
assisting the cooling?  I can believe with the doors off
that it's going to move that much air from the bottom of the rack.  Or is it
to pull heat from the "stack" of machines?
I'm just trying to understand this....  In my head I was thinking having the
doors would help the top fans pull air from the
bottom.  But I hadn't thought about the way they'd also hold in heat from
all the machines, and that you'd get that hot air
exhaust coming around and re-circulating thru the machines.  Very very
helpful to know that that happens....

Also, if I have any open space in the rack, I should bunch it up... I'm
thinking it should be near the top.... or does
it really matter where it is?

In all cases, I really appreciate the advise, real world data, and modeling
results!  Way cool... and really helps to
bust the myths that we all build up in our heads...

Earl