If you have raised-floor cooling, how do you like to arrange airflow for a cabinet with a single bladeserver chassis? You could have a nice big hole under the cabinet, with the bladeserver mounted low. It would suck the chilled air up and to the front edge of the cabinet, then shoot exhaust out the back. This might work best with a solid front panel (but that hole had better be big!).
Or you could leave the floor closed under the cabinet; have a perforated tile in the cold row right in-front of the bladeserver chassis, and use a mesh front panel on the cabinet. I'm not sure which would draw more air from the floor: up from under the cabinet, or up from in front of the cabinet, then in through the cabinet door.
What would you do for 2 or more bladeserver chassies? With a full cabinet of bladeservers, it seems pretty pointless to try to get chilled below-floor air up to the top of the cabinet. You're going to suck ambient air, no matter how you slice it.
Are there situations where you'd add APC's "floor sucker" Rack Air Distribution fans? Or cabinet-top exhaust fans? They seem pointless with bladeservers and a mesh-front cabinet (?), but maybe with a solid front panel and a gaping hole under the cabinet, they might work better than just letting the bladeserver fans do the work?
Cooling blade servers in a raised flooring environment is a challenge, ambient cooling is easier. I would suggest you have a mesh door in the back of the cabinet and a solid door on the front with a large fan on the top of the cabinet. You may want to stick a couple of temperature sensors at different levels of the cabinet so you can monitor.
I have no hard data to give you, but in my experience, the more holes you put in the floor under racks the more difficult it will be to maintain enough static pressure underfloor to direct the cooling air where you want it to go. If you leave all your tile cuts open or intentionally cut large openings you end up with the cooling air leaking out all over the place in the wrong place and underfloor static pressure drops, messing up your hot aisle/cold aisle layout. If the hardware is cooled front to back as most is, mesh rack fronts and rears combined with a perf tile or grille should be able to direct the chilled air where you want it - at the front of the rack to be passed through the hardware and out the back into the hot aisle. More blades in the same rack make it more important that you maintain the static pressure so the air can make the distance from the floor to the upper portion of the rack. Rather than perf tiles, you can use grilles that contain turning veins that can be slightly angled toward the rack and so help deliver the cooling air where you want it - as long as the static pressure is maintained. Remember that the chilled air is the 'ambient air' you want flowing through the hardware - from underfloor then front to back through the hardware, not the heated air from the rear of the rack. I think the top mounted fan packs are only useful in racks with closed fronts and they are normally equipped with intake grilles on the lower front portion of the rack - so the 'cold aisle front' rule still applies. The hardware fans are supposed to do the work, that's why they are there.
This topic was the focus of a lot of discussion on panels at both AFCOM and DataCenterDynamics conferences the past two weeks in recent weeks. Here's a couple of articles that summarize some of the discussions:
To cool down blades in a rack, you can still use the conventional cooling approach of having perf tiles in front with the server rack with fully perforated doors front and back. As long as you sufficient cooling capacity from your cracs there is no problem cooling racks having up to 8kw to 10 kw heat dissipation. The key to this is to have sufficient supply air flow from the cold aisle in front of the blade rack. and CRAC cooling capacity.
I have installed 4 racks in a row fully loaded with dual CPU -1U servers with up to 8 kw per rack.
I ended-up mounting the bladeserver chassis down low, with a perf tile in the cold aisle for each bladeserver (maybe overkill). It seems to be doing fine.
I ended-up mounting the bladeserver chassis down low, with a perf tile in the cold aisle for each bladeserver (maybe overkill). It seems to be doing fine.
A good choice -- I think this is your best strategy. I hope you're using server cabinets with perf'ed front and rear doors. Also, make sure the blades don't "starve" equipment mounted higher in the racks. Equipment demands about 140 cfm/kW, so your cold aisle needs to deliver that. Be careful how you load your racks; if the load is too dense, you'll have problems with them rebreathing air from the hot aisle -- over the top or around the sides.
Zitibake,
KenB makes a very valid point in pointing out that you do not want to starve the equipment of cold air supply mounted higher.
The blade servers I have racked I chose to rackmount mid cabinet to allow the air flow to come from more than just 1 floor tile. My hope is to allow the ambient temperature of the cold aisle to pull air in to the blade chassis will still allowing servers with a lower air flow rate to still benefit. By having the blades down at the bottom of the cabinet, they have the ability to suck air like a vacuum due to their increased fan speeds. The dell blades I have used have 2 chassis fans that will blow the toupee off of any old man as well as 4 power supply fans capable of doing about the same. This high volume of air all comes from the front. So unless your floor tiles have the ability to send your toupee flying, these will suck a significant amount of air more than what your tiles are delivering which means it is also going to suck the rest from ambient.
In summary, I wanted to be sure that I cooled the ambient down as much as possible, in the cold aisle, to ensure everything gets a fair dose of cool ambient.
Another thing I would consider. If you are giving your coolest air to the blades, they will not run near as hot in the hot aisle. This will cause for hyper-cooled air to hit the back of the cabinet which will not rise out of the hot aisle as efficiently. It is not necessary to run a blade server at 64 degrees if the blades are not going to be heavily used. If you start to have issues with other things getting a little warmer, I would monitor the internal chassis temperature sensors to determine if they are running cool inside and consider moving them a little higher up.
If you have the extra rack space, I would put blank panels under the areas under the blade chassis.
If these racks are in a facility that you own, I would also perhaps make sure that you have 2 full floor tiles in width in your cold aisle. This will allow you to populate more cold air to ensure that cold aisle ambient temperatures get to the cabinet; this would be a recommendation if you have a lot of these blade chassis. One caviat is that once you increase the cool areas, you will have to make sure your hot air return is much more efficient to mitigate hot air recirculation.
raised floor cooling plus bladeservers?
