nanog mailing list archives
Re: Rasberry pi - high density
From: Brandon Martin <lists.nanog () monmotha net>
Date: Mon, 11 May 2015 18:50:59 -0400
On 05/11/2015 06:21 PM, Randy Carpenter wrote:
That is .8-1.6A at 5v DC. A far cry from 120V AC. We're talking ~5W versus ~120W each. Granted there is some conversion overhead, but worst case you are probably talking about 1/20th the power you describe.
His estimates seem to consider that it's only 5V, though. He has 825 Pis per rack at ~5-10W each is call it ~8kW on the high end. 8kW is 2.25 tons of refrigeration at first cut, plus any power conversion losses, losses in ducting/chilled water distribution, etc. Calling for at least 3 tons of raw cooling capacity for this rack seems reasonable.
8kW/rack is something it seems many a typical computing oriented datacenter would be used to dealing with, no? Formfactor within the rack is just a little different which may complicate how you can deliver the cooling - might need unusually forceful forced air or a water/oil type heat exchanger for the oil immersion method being discussed elsewhere in the thread.
You still need giant wires and busses to move 800A worth of current. It almost seems like you'd have to rig up some sort of 5VDC bus bar system along the sides of the cabinet and tap into it for each shelf or (probably the approach I'd look at first, instead) give up some space on each shelf or so for point-of-load power conversion (120 or 240VAC to 5VDC using industrial "brick" style supplies or similar) and conventional AC or "high voltage" (in this context, 48 or 380V is "high") DC distribution to each shelf. Getting 800A at 5V to the rack with reasonable losses is going to need humongous wires, too. Looks like NEC calls for something on the order of 800kcmil under rosy circumstances just to move it "safely" (which, at only 5V, is not necessarily "effectively") - yikes that's a big wire.
-- Brandon Martin
Current thread:
- Re: Rasberry pi - high density, (continued)
- Re: Rasberry pi - high density Eugeniu Patrascu (May 09)
- Re: Rasberry pi - high density Nick B (May 09)
- Re: [eX-bulk] : Re: Rasberry pi - high density nanog (May 14)
- Re: [eX-bulk] : Re: Rasberry pi - high density charles (May 14)
- Re: Rasberry pi - high density Eugeniu Patrascu (May 09)
- Re: Rasberry pi - high density Dave Taht (May 09)
- Re: Rasberry pi - high density Clay Fiske (May 11)
- Re: Rasberry pi - high density Dave Taht (May 11)
- Re: Rasberry pi - high density Peter Baldridge (May 11)
- Re: Rasberry pi - high density Randy Carpenter (May 11)
- Re: Rasberry pi - high density Peter Baldridge (May 11)
- Re: Rasberry pi - high density Brandon Martin (May 11)
- Re: Rasberry pi - high density Lamar Owen (May 13)
- Re: Rasberry pi - high density Dave Taht (May 11)
- Re: Rasberry pi - high density Chris Boyd (May 11)
- Re: Rasberry pi - high density Rafael Possamai (May 11)
- Re: Rasberry pi - high density Hugo Slabbert (May 11)
- Re: Rasberry pi - high density Rafael Possamai (May 11)
- Re: Rasberry pi - high density Joel Maslak (May 11)
- Re: Rasberry pi - high density Rafael Possamai (May 12)