[Beowulf] Newbie Question: Racks versus boxes and good rack solutions for commodity hardware

arjuna brahmaforces at gmail.com
Mon Dec 15 00:45:35 EST 2008


Robert:

Thanks for the practical and good advice... I see what you are saying...When
I was a child i did play with electrical circuits and tried to build a radio
out a PCBs components and a soldering iron, needless to say, without proper
guidance or google at that time, after months of inspired tinkering, i never
got the radios to recieve anything.However it did give me a basic awareness
and handling of electrical components, soldering irons and so on..

I understand insulators and conductors. Yes i should do some basic
electronic study and that would be very interesting. Any groups online for
the same or landmark books or hobby kits that you may have encountered
growing up or earlier in your careers would be appreciated...

The only reason I mention "Alumninum" was because I noticed that the
motherboards in the tower cases were stuck onto some metal and my hardware
person told me that this is a special material that does not conduct
electricity. And since everyone was taking about aluminum boards here,  i
put 2 and 2 together, and obviously instead of 4 I got 10...

Given that we are working with a stepped down voltage the risk is lower,
however since we are creating a system, it would  make sense to make it
entirely safe. Wood like you said is a fire hazard,  aluminum conducts
electricity.

Then in your experience, what would be the right material to use to avoid
electrical and fire hazards, assuming its not a space ship kevelar or other
impossible to find substance or one that is prohibitively expensive.

I realize i have a learning curve with:

1) Building computer hardware
2) Electronics

I will now attempt to read up and practise both of the above by assembling a
computer and finding some basic electronic books and materials to assemble.

In the mean time I do want to make a 1 U system that i dreamed of last
night, where 3 mother boards go on 1 plate (assuming the right material and
precautions to make it safe) This plate goes in some kind of casing for
safety for now, later to be removed and put into a rack...

Then its time to play with the parrallel processing software....

On Sun, Dec 14, 2008 at 10:40 PM, Robert G. Brown <rgb at phy.duke.edu> wrote:

> On Sat, 13 Dec 2008, arjuna wrote:
>
>  A simple question though...Aluminum plates are used because aluminum is
>> does
>> not conduct electricity. Is this correct?
>>
>
> Aluminum is an EXCELLENT conductor of electricity, one of the best!
> Basically all metals conduct electricity.  When you mount the
> motherboards you MUST take care to use spacers in the right places
> (under the holes for mounting screws on the motherboards, usually) to
> keep the solder traces of the motherboard from shorting out!
>
> Your question makes me very worried on your behalf.  Electricity is
> quite dangerous, and in general messing with it should be avoided by
> anyone that does not already know things like this.  In India, with 240
> VAC as standard power, this is especially true.  True, the power
> supplied to the motherboards is in several voltages 12V and under, but
> believe it or not you can kill yourself with 12V, and starting a fire
> with 12V is even easier.
>
> I would >>strongly<< suggest that you find a friend with some electrical
> engineering experience, or read extensively on electricity and
> electrical safety before attempting any sort of motherboard mount.
> Mark's suggestion of hot melt glue, for example, is predicated on your
> PRESUMED knowledge that cookie sheets or aluminum sheets are
> conductors, that the motherboard has many traces carrying current, and
> that when you mount the motherboard you must take great care to ensure
> that current-carrying traces CANNOT come in contact with metal.
>
> The reasons aluminum plates are suggested are a) it's cheap; b) it's
> easily drilled/tapped for screws; c) it's fireproof AS LONG AS YOU DON'T
> GET IT TOO HOT (heaven help you if you ever do start it on fire, as it
> then burns like thermite -- oh wait, thermite IS aluminum plus iron
> oxide); d) it reflects/traps EM radiation.
>
> Wood would be just as good except for the fireproof bit (a big one,
> though -- don't use wood) and the EM reflecting part.
>
> The aluminum plates should probably all be grounded back to a common
> ground.  The common ground should NOT be a current carrying neutral --
> I'm not an expert on 240 VAC as distributed in India and hesitate to
> advise you on where/how to safely ground them.  You should probably read
> about "ground loops" before you mess with any of this.
>
> Seriously, this is dangerous and you can hurt yourself or others if you
> don't know what you are doing.  You need to take the time to learn to
> the point where you KNOW how electricity works and what a conductor is
> vs an insulator and what electrical codes are and WHY they are what they
> are before you attempt to work with bare motherboards and power
> supplies.  It is possible to kill yourself with a nine volt transistor
> radio battery (believe it or not) although you have to work a bit to do
> so.  It is a lot easier with 12V, and even if you don't start a fire,
> you will almost certainly blow your motherboard/CPU/memory and power
> supply if you short out 12V in the wrong place.
>
>  Also for future reference, I saw a reference to dc-dc converters for power
>> supply. Is it possible to use motherboards that do not guzzle electricity
>> and generate a lot of heat and are yet powerful. It seems that not much
>> more
>> is needed that motherboards, CPUs, memory, harddrives and an ethernet
>> card.
>> For a low energy system, has any one explored ultra low energy consuming
>> and
>> heat generating power solutions that maybe use low wattage DC?
>>
>
> The minimum power requirements are dictated by your choice of
> motherboard, CPU, memory, and peripherals.  Period.  They require
> several voltages to be delivered into standardized connectors from a
> supply capable of providing sufficient power at those voltages.  Again,
> it is clear from your question that you don't understand what power is
> or the thermodynamics of supplying it, and you should work on learning
> this (where GIYF).  As I noted in a previous reply, typical motherboard
> draws are going to be in the 100W to 300+W loaded, and either you
> provide this or the system fails to work.  To provide 100W to the
> motherboard, your power supply will need to draw 20-40% more than this,
> lost in the conversion from 120 VAC or 240 VAC to the power provided to
> the motherboard and peripherals.  Again, you have no choice here.
>
> The places you do have a choice are:
>
>  a) Buying motherboards etc with lower power requirements.  If you are
> using recycled systems, you use what you've got, but when you buy in the
> future you have some choice here.  However, you need to be aware of what
> you are optimizing!  One way to save power is to run at lower clock, for
> example -- there is a tradeoff between power drawn and speed.  But
> slower systems just mean you draw lower power for longer, and you may
> well pay about the same for the net energy required for a computation!
> You need to optimize average draw under load times the time required to
> complete a computation, not just "power", weighted with how fast you
> want your computations to complete and your budget.
>
>  b) You have a LIMITED amount of choice in power supplies.  That's the
> 20-40% indicated above.  A cheap power supply or one that is incorrectly
> sized relative to the load is more likely to waste a lot of power as
> heat operating at baseline and be on the high end of the power draw
> required to operate a motherboard (relatively inefficient).  A more
> expensive one (correctly sized for the application) will waste less
> energy as heat providing the NECESSARY power for your system.
>
> That is, you don't have a lot of choice when getting started -- you're
> probably best off just taking the power supplies out of the tower cases
> of your existing systems and using them (or better, just using a small
> stack of towers without remounting them until you see how clustering
> works for you, which is safe AND effective).  When you have done some
> more research and learned about electricity, power supplies, and so on
> using a mix of Google/web, books, and maybe a friend who works with
> electricity and is familiar with power distribution and code
> requirements (if any) in New Delhi, THEN on your SECOND pass you can
> move on to a racked cluster with custom power supplies matched to
> specific "efficient" motherboards.
>
>   rgb
>
>
>
>> On Sat, Dec 13, 2008 at 8:50 AM, Mark Hahn <hahn at mcmaster.ca> wrote:
>>            What is 1u?
>>
>>
>>      rack-mounted hardware is measured in units called "units" ;)
>>      1U means 1 rack unit: roughly 19" wide and 1.75" high.  racks
>>      are all
>>      the same width, and rackmount unit consumes some number of units
>>      in height.
>>      (rack depth is moderately variable.)  (a full rack is generally
>>      42").
>>
>>      a 1U server is a basic cluster building block - pretty well
>>      suited,
>>      since it's not much taller than a disk, and fits a motherboard
>>      pretty nicely (clearance for dimms if designed properly, a
>>      couple optional cards, passive CPU heatsinks.)
>>
>>            What is a blade system?
>>
>>
>> it is a computer design that emphasizes an enclosure and fastening
>> mechanism
>> that firmly locks buyers into a particular vendor's high-margin line
>> ;)
>>
>> in theory, the idea is to factor a traditional server into separate
>> components, such as shared power supply, unified management, and often
>> some semi-integrated network/san infrastructure.  one of the main
>> original
>> selling points was power management: that a blade enclosure would have
>> fewer, more fully loaded, more efficnet PSUs.  and/or more reliable.
>> blades are often claimed to have superior managability.  both of these
>> factors are very, very arguable, since it's now routine for 1U servers
>> to have nearly the same PSU efficiency, for instance.  and in reality,
>> simple managability interfaces like IPMI are far better (scalably
>> scriptable)
>> than a too-smart gui per enclosure, especially if you have 100
>> enclosures...
>>
>>      goes into a good rack in terms of size and matieral
>>      (assuming it has to be
>>      insulated)
>>
>>
>> ignoring proprietary crap, MB sizes are quite standardized.  and since
>> 10 million random computer shops put them together, they're incredibly
>> forgiving when it comes to mounting, etc.  I'd recommend just
>> glue-gunning
>> stuff into place, and not worring too much.
>>
>>      Anyone using clusters for animation on this list?
>>
>>
>> not much, I think.  this list is mainly "using commodity clusters to
>> do stuff fairly reminiscent of traditional scientific supercomputing".
>>
>> animation is, in HPC terms, embarassingly parallel and often quite
>> IO-intensive.  both those are somewhat derogatory.  all you need to do
>> an animation farm is some storage, a network, nodes and probably a
>> scheduler or at least task queue-er.
>>
>>
>>
>>
>> --
>> Best regards,
>> arjuna
>> http://www.brahmaforces.com
>>
>>
>>
> Robert G. Brown                        http://www.phy.duke.edu/~rgb/<http://www.phy.duke.edu/%7Ergb/>
> Duke University Dept. of Physics, Box 90305
> Durham, N.C. 27708-0305
> Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu<email%3Argb at phy.duke.edu>
>
>


-- 
Best regards,
arjuna
http://www.brahmaforces.com

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