6 ms·

>>> A single fan running at full speed consumes about 40W I thought fans consumed like 10 times less

by fasteo 3y ago

temp0826 3y ago
A normal fan in your home PC yes. Not the 40mm jet engines you only find in data centers.
- buildbot 3y ago
  Yeah some of these fans are capable of lifting off helicopter style…
- amluto 3y ago
  I’m a bit surprised the big datacenter / OpenCompute buyers haven’t moved toward a form factor that’s more square. Big, high-power, quiet desktop systems have been using monster fans for many years, and ISTM one could do better with systems that are maybe 4U high but only half width, enabling a proper fan in back. Or maybe even a form factor that’s packs a lot of individual machines in front of a full width truly immense fan (19” or more!).
  - jeffrallen 3y ago
    In 1999, Tellme was using square servers from Dialogic, a vendor of PCI Telco cards.
  - Voultapher 3y ago
    Oxide Computer has for their systems. Could be a trend.
  - wmf 3y ago
    Facebook/Meta has been using 2OU (which is slightly taller than 2U) for years. Oxide also uses 2U.
  - amluto 3y ago
    Time for real data! Here's a nice line of modern server fans: https://www.delta-fan.com/newspost/ingress-protection-ip55-ip56-durable-reliable-and-weatherproof-7.html https://www.delta-fan.com/newspost/ingress-protection-ip55-i... 40mm, 12.6W gets 21.56cfm (at zero pressure) or 3.416 inH2O (at zero flow). That's 1.7 cfm/W. 140mm, 46.8W gets 282.31cfm or 2.033 inH2O. That's 6.03 cfm/W, over 3x better. Now, I'm being a bit unfair: I ignored pressure. I don't see fan curves, but a vaguely credible figure of merit if we're just trying to estimate efficiency is to multiple the flow and the pressure and divide by power. The little fan gets 0.68 and the big fan gets 1.44. That's still quite a lot better. (It does not mean that fan exceeds 100% efficiency. It's not delivering 282.31cfm at 2.033 in H2O.) But, interestingly, these fans produce almost the same velocity. If the moderately lower available pressure from the large fan isn't a problem (which it shouldn't be -- we're talking about a regime where there is too much TDP per rack, so it's beneficial to spread things out, thus reducing resistance to airflow), these fans really can substitute for each other in the sense that covering the same area with big fans produces about the same airflow as covering the area with small fans. Oh, and the big fan is louder, but not louder than 10 small fans! So I stand by my claim: if you are cooling the contents of your rack by filling it with metal tubes and blowing air through the tubes using fans, use big fans, which you can achieve by using taller units. And 2U isn't enough for that 140mm fan.

>>> A single fan running at full speed consumes about 40W I thought fans consumed like 10 times less

by fasteo 3y ago

>>> A single fan running at full speed consumes about 40W I thought fans consumed like 10 times less

temp0826 3y ago

A normal fan in your home PC yes. Not the 40mm jet engines you only find in data centers.

buildbot 3y ago
Yeah some of these fans are capable of lifting off helicopter style…
amluto 3y ago
I’m a bit surprised the big datacenter / OpenCompute buyers haven’t moved toward a form factor that’s more square. Big, high-power, quiet desktop systems have been using monster fans for many years, and ISTM one could do better with systems that are maybe 4U high but only half width, enabling a proper fan in back. Or maybe even a form factor that’s packs a lot of individual machines in front of a full width truly immense fan (19” or more!).
- jeffrallen 3y ago
  In 1999, Tellme was using square servers from Dialogic, a vendor of PCI Telco cards.
- Voultapher 3y ago
  Oxide Computer has for their systems. Could be a trend.
- wmf 3y ago
  Facebook/Meta has been using 2OU (which is slightly taller than 2U) for years. Oxide also uses 2U.
- amluto 3y ago
  Time for real data! Here's a nice line of modern server fans: https://www.delta-fan.com/newspost/ingress-protection-ip55-ip56-durable-reliable-and-weatherproof-7.html https://www.delta-fan.com/newspost/ingress-protection-ip55-i... 40mm, 12.6W gets 21.56cfm (at zero pressure) or 3.416 inH2O (at zero flow). That's 1.7 cfm/W. 140mm, 46.8W gets 282.31cfm or 2.033 inH2O. That's 6.03 cfm/W, over 3x better. Now, I'm being a bit unfair: I ignored pressure. I don't see fan curves, but a vaguely credible figure of merit if we're just trying to estimate efficiency is to multiple the flow and the pressure and divide by power. The little fan gets 0.68 and the big fan gets 1.44. That's still quite a lot better. (It does not mean that fan exceeds 100% efficiency. It's not delivering 282.31cfm at 2.033 in H2O.) But, interestingly, these fans produce almost the same velocity. If the moderately lower available pressure from the large fan isn't a problem (which it shouldn't be -- we're talking about a regime where there is too much TDP per rack, so it's beneficial to spread things out, thus reducing resistance to airflow), these fans really can substitute for each other in the sense that covering the same area with big fans produces about the same airflow as covering the area with small fans. Oh, and the big fan is louder, but not louder than 10 small fans! So I stand by my claim: if you are cooling the contents of your rack by filling it with metal tubes and blowing air through the tubes using fans, use big fans, which you can achieve by using taller units. And 2U isn't enough for that 140mm fan.