[Beowulf] A Cluster of Motherboard.

Jim Lux James.P.Lux at jpl.nasa.gov
Thu Nov 10 13:10:38 EST 2005


At 07:59 AM 11/10/2005, Robert G. Brown wrote:
>On Thu, 10 Nov 2005, Josip Loncaric wrote:
>
>>A cheap bare case can cost less than $20 -- and can save you a lot of 
>>work, although perhaps not shelf space.  For safety, ease of 
>>installation, and FCC EM reasons, cheap metal cases should be considered.
>
>Yeah, I think that Jim's observation that you should think carefully
>about the diminishing returns of building a freeform caseless cluster is
>very apropos -- you'll save a bit of money on space and cases -- maybe
>-- at the expense of more hands on work building the cluster and at the
>risk of having to resolve problems with shielding and so on.  For a
>>>professional<< grade cluster I'd generally not recommend this approach
>unless you are truly working with a shoestring budget and have a metal
>shop handy or are building a hobby/learning cluster and want the entire
>cluster to be "visible" and supercheap.
>
>In this latter case, you can probably get by by taking sheets of steel
>or aluminum, drilling them out using the mounting holes of the
>motherboard as a template, and mounting the motherboards on them using
>the standard spacers and screws just LIKE a case.  You can then get
>creative in several ways as to just how you insert the plates into metal
>shelving or even a metal file cabinet drawer with suitably mounted fans
>so that each board is cooled, powered, and still reasonably well EM
>shielded from the others.  I doubt that you'll save much money (I'm
>CERTAIN you won't save money if you bill your own time into the project
>even at minimum wage and you'll lose big if you "charge" the
>$50-100/hour your time is probably worth:-).


I just looked at a motherboard here.  9 holes.  Figure you can "gang drill" 
about an inch worth of plates at once, call it a dozen, on a drill 
press.  Probably about 30-60 minutes to set up and mark it, do the 
drilling, clean it up, deburr the holes, etc.  Assume aluminum so you don't 
have to paint it.  Now, you have to find about 200 screws and washers, 100 
standoffs, etc.  If you're smart, and set up a little jig, you can probably 
drive a couple screws a minute, so there's about 3 hours or so, by the time 
you count fooling around getting the parts organized, etc.

You also have to drill holes to mount the drives and power supplies, etc.

You're probably pretty close to half an hour per system.  Figure $5 in 
labor, plus you've got material costs.  That $20 stamped sheetmetal case is 
looking pretty darn attractive.


There IS a faster way, for a bare system approach.  Use double sided sticky 
foam tape.  Plenty strong, it will last 2 or 3 years.





>One other thing to watch that I think that Jim brushed up against is
>your power supply wiring and ground vs neutral.  If you have three or
>four power supplies, each plugged into a different circuit, those
>circuits can easily have different phases.  If you are not careful and
>do not know what you are doing, there are a variety of ways to create
>spectacularly dangerous conditions -- ground loops and worse -- where by
>spectacular I mean that "when you plug it in it will explode in a shower
>of vaporized and melted metal".  Cases and case power supplies are
>designed to be pretty safe -- plug it in and snap on connectors that
>really can only work one way.  If you go anywhere beyond this, I'd
>REALLY recommend that you only proceed if you completely understand
>electricity and electrical wiring and know what a ground loop IS and so
>on.

That's just part of the thrill of bareboard wiring.  True expertise and 
learning only comes from a good near death experience.


>     rgb


Jim


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