Wow Ken, that is quite the list!
Here is another long post from me... Please bare with me!
Neo,
There are a couple of critical items that Ken mentioned that I stress upon every datacenter manager I come across. I dumbed down my section a bit for general purposes since it is all not aimed directly at you. I am sure you probably don't need as much detail as I am providing; since a lot of it is common sense.
1) Perforated tiles... I do not know why people make it so that the entire floor is perforated! Use only the amount that is needed. Air flow will suck unless pressure is able to build under the floor. I also notice that customers of mine tend to put perforated tiles in the hot aisle... They are called hot aisles for a reason... Putting positive pressure on a row full of hot air will only cause the hot air to move to places of lesser pressure. Also, it wont kill you pay less attention to cooling the "ambient" spaces of the datacenter. By this, I mean take out perforated tiles that are in common areas and/or large open spaces not occupied by running equipment. This will allow you to force more air which will cause the servers to output lower temperature air.
2) Spacer Blanks... Should you use them? Absolutely! I am torn on whether or not to put a space between all of the servers (and having a blank panel) or having the servers stacked together with blanks on the remainder of the open space above and below the servers. Heres my internal debate...You stack the servers on top of each other without spacing in between and you have the possibility for thermal heat transfer. If you stack them with a 1u gap and 1u blank panel, the air will still accumulate (but not recirculate) in those voids. So the difference between the 2... Thermal transfer of course can be a concern... My bigger concern is the rebreathing that is common across all datacenters.
Now I have a few additions that I would like to add.
1) Cable management... One thing I will admit to is being anal retentive when it comes to cabling and the general maintenance of the back of server racks. How is your cabling? Is it managed? Are there large bundles of wire that may restrict some exhaust? Air can't go in unless air can come out first.
2) Cabinet Doors... While I can admit that putting doors on cabinets sure is perty, I am a firm believer in not using them if you have airflow issues. The airflow resistance on a cabinet increases a significant amount with the doors closed; especially in the back of the cabinet. Like cables, the cabinet doors on the back of the rack may cause the hot air to not be fully expelled from the cabinet and in to the hot aisle for recirculation.
3) Side panels... My belief on cabinet side panels is that they were invented with panels on the side for a reason. While it may be convenient for running cables between racks (without using a tray of some sort), it opens up a lot of potential for the ever so famous rebreathing theory. Many new cabinets have cutouts on the sides for routing cables through the side panels.
4) Properly manage your space plan. Its a balancing act, one that I quite enjoy playing at times. Take inventory of your space plan and balance servers/racks around the datacenter until you get a balance. One datacenter I was working in had a large customer move out. They were extremely high density (80 servers per rack). When they moved out, I was in their old space trying to set it up for a new customer, I set my build sheet down on my ladder and the second I let go, it went flying away. The airflow from the ceiling vents was that rediculously strong. On the other side of the building, we had warm spots. We cranked down the jet and the hot spots went away.
5) (Holy crap this is a lot of typing) CRAC maintenance... Check your filters! Clogged filters = crap air flow. If only Dyson made CRAC units, they wouldn't lose suction due to clogged filters.
Have your CRAC units properly inspected and maintained, make sure the fan is functioning properly, and make sure the system is adequately charged with freon, glycol, or whatever... Oh and for the love of god, clean up what is under the floor! Resistance is your worst nightmare.