[Beowulf] FW: let's standardize liquid cooling

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Fri Sep 28 15:13:15 PDT 2012



Jim Lux

-----Original Message-----
From: Lux, Jim (337C) 
Sent: Friday, September 28, 2012 2:40 PM
To: Lux, Jim (337C)
Subject: RE: [Beowulf] let's standardize liquid cooling

And here we go with the low budget approach to large diameter fan cooling of many nodes:

Eschew conventional chassis.  Use an $8  18x26" aluminum sheet pan: http://www.foodservicewarehouse.com/thunder-group/alsp1826m/p548194.aspx

Attaching the mother board and other equipment to the pan with double stick foam tape: http://www.3m.com/product/information/VHB-Acrylic-Foam-Tape.html
(most expensive single component is the tape)

Supported by 20 tier rolling racks: http://www.foodservicewarehouse.com/channel-mfg/401akd/p349120.aspx
(about $100)

With an array of 3 each 20" box fans on either side of the rack as needed. (or front and back..) (about $16 each.. and heavily discounted this time of year)

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?productId=100405665&storeId=10051&langId=-1&catalogId=10053&ci_sku=100405665&ci_kw={keyword}&kwd={keyword}&cm_mmc=shopping-_-googleads-_-pla-_-100405665&ci_gpa=pla#.UGYXiFHvy4g

Note they claim 2500 CFM flow (per fan).
Those little 25-35 mm fans push maybe 1 CFM.  Stack 40 U high, and 10 across, and you're still only at 400 CFM.  

Maybe they don't look as pretty as 19" racks, but face it, with a 19" rack and conventional sheet metal chassis, you're buying LOT of metal that you don't really need in this application.  Once the node is in the cabinet, why does it need a box around it? 

You could make a very pretty looking version of my bakery rack scheme.  Rolled edge pans with prepunched holes for the motherboard on standoffs, etc. Solid sides and doors with integrated fans.

A lot of the weight in a conventional rack is there for structural reasons.. to hold up the sheetmetal boxes around the motherboards.  The mobos themselves weigh very little, after all.




Jim Lux


-----Original Message-----
From: beowulf-bounces at beowulf.org [mailto:beowulf-bounces at beowulf.org] On Behalf Of Lux, Jim (337C)
Sent: Friday, September 28, 2012 2:26 PM
To: Bill Broadley; beowulf at beowulf.org
Subject: Re: [Beowulf] let's standardize liquid cooling

An interesting idea..
BUT.. you might need some sort of "bench test" fixture.. thermally driven convection might work.

And I think you'd have mfrs worried about people filling a rack full of fanless nodes and then not turning on the fans.  Or the power failing to the fans, or, opening both doors.

I suppose some sort of overtemperature cutout would solve this: the mobo would just shut down if it got too hot.


Whatever happened to a Beowulf made of tower cases piled on brick and board book cases?

Or this incredibly adaptable scheme: http://climate.ornl.gov/~forrest/linux-magazine-1999/  note the easy reference information inscribed on each node in this novel heterogenous cluster.  It's all part of addressing: "Management of such a large, heterogeneous cluster poses many challenges."

Jim Lux


-----Original Message-----
From: beowulf-bounces at beowulf.org [mailto:beowulf-bounces at beowulf.org] On Behalf Of Bill Broadley
Sent: Friday, September 28, 2012 2:15 PM
To: beowulf at beowulf.org
Subject: Re: [Beowulf] let's standardize liquid cooling


Sounds expensive, complicated, and challenging.

How about a MUCH simpler proposal: eliminate fans from compute nodes.

Nodes should:
* assume good front to back airflow

Racks would:
* have large fans front AND back that run at relatively low
  rpm, and relatively quiet.
* If front or rear door open the other door would ramp up fans
  (and noise) to compensate.

My measurements of 1U nodes have shown a significant fraction of the power budget goes to fans!  Fans that fit in 1U (even 2U) nodes seem to generate more noise, heat, and vibration than airflow.


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