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Seems like you could have gotten higher density going vertical instead of horizontal. It would have been 50% taller (6U instead of 4U) but it could have held 1

Seems like you could have gotten higher density going vertical instead of horizontal. It would have been 50% taller (6U instead of 4U) but it could have held 100% more Mac Pros. A Mac Pro is 9.9 inches tall and 6.6 inches in diameter. 9.9 / 1.75 = 5.65 and 6.6 / 1.75 = 3.77 https://www.apple.com/mac-pro/specs/ https://www.apple.com/mac-pro/specs/

skuhn 12y ago
This was one of our initial ideas for the design, but it boiled down to an airflow concern. There are some products that do this, such as http://www.h-sq.com/products/mprack/index.html http://www.h-sq.com/products/mprack/index.html If you look at how the airflow works on that shelf, I think you'll see why I don't have confidence in that solution. The air paths to each system seem to be based on wishful thinking. We also didn't need to go that dense after considering each host's power draw at full load. I design towards a 208v/3ph/50a circuit on each rack, and 44 Mac Pros at full load (plus a switch) are about 13.5kW in my testing. So we would need to build for 60A circuits, or not completely fill the rack, to make the vertical orientation worthwhile.
- msandford 12y ago
  That product you linked to isn't all that bad, provided that you run with a front plate to actually block off the rest of the cold isle and force the air to flow to the hot isle. But that doesn't seem to be included anywhere. So I agree that it's wishful thinking. The reality of the power budget makes the most sense really. There's no point in cramming extra units in if you're going to have to rewire for them. Systems engineering!
  - skuhn 12y ago
    H-Squared's product isn't terrible by any means, but I see it as phase 1 of at least a 2 or 3 phase solution. If you were running one shelf of Pros in a rack, it wouldn't matter much -- but at 10 racks of 88 Pros each, you'll run into cooling issues unless you put more work into it. On the topic of density: our chassis was originally specced to support 6 units rather than 4. I vetoed that because it would require a second top-of-rack switch, and would have been too power dense for our current site design. 44 turned out to be the magic number this time around. The design is also flexible enough that if the specification changes dramatically in future Mac Pros, we can tweak as necessary to achieve ideal density.
apendleton 12y ago
I suspect that the sideways orientation is motivated by cooling. The mac pro sucks air in the bottom and shoots it out the top, so if you stack them, the top machine is sucking in the bottom machine's hot air. In this orientation, the whole rack is sucking air in from one exposed side and pushing it out the other exposed side; much easier to engineer around.
- skuhn 12y ago
  You're right, it is entirely about airflow.
karmakaze 12y ago
Except that this would put the hot chambers next to the cold ones of the next layer.

skuhn 12y ago

This was one of our initial ideas for the design, but it boiled down to an airflow concern. There are some products that do this, such as http://www.h-sq.com/products/mprack/index.html http://www.h-sq.com/products/mprack/index.html If you look at how the airflow works on that shelf, I think you'll see why I don't have confidence in that solution. The air paths to each system seem to be based on wishful thinking. We also didn't need to go that dense after considering each host's power draw at full load. I design towards a 208v/3ph/50a circuit on each rack, and 44 Mac Pros at full load (plus a switch) are about 13.5kW in my testing. So we would need to build for 60A circuits, or not completely fill the rack, to make the vertical orientation worthwhile.

msandford 12y ago
That product you linked to isn't all that bad, provided that you run with a front plate to actually block off the rest of the cold isle and force the air to flow to the hot isle. But that doesn't seem to be included anywhere. So I agree that it's wishful thinking. The reality of the power budget makes the most sense really. There's no point in cramming extra units in if you're going to have to rewire for them. Systems engineering!
- skuhn 12y ago
  H-Squared's product isn't terrible by any means, but I see it as phase 1 of at least a 2 or 3 phase solution. If you were running one shelf of Pros in a rack, it wouldn't matter much -- but at 10 racks of 88 Pros each, you'll run into cooling issues unless you put more work into it. On the topic of density: our chassis was originally specced to support 6 units rather than 4. I vetoed that because it would require a second top-of-rack switch, and would have been too power dense for our current site design. 44 turned out to be the magic number this time around. The design is also flexible enough that if the specification changes dramatically in future Mac Pros, we can tweak as necessary to achieve ideal density.

apendleton 12y ago

I suspect that the sideways orientation is motivated by cooling. The mac pro sucks air in the bottom and shoots it out the top, so if you stack them, the top machine is sucking in the bottom machine's hot air. In this orientation, the whole rack is sucking air in from one exposed side and pushing it out the other exposed side; much easier to engineer around.

skuhn 12y ago
You're right, it is entirely about airflow.

karmakaze 12y ago

Except that this would put the hot chambers next to the cold ones of the next layer.