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

Robert G. Brown rgb at phy.duke.edu
Mon Dec 15 01:05:01 EST 2008


On Mon, 15 Dec 2008, arjuna wrote:

> 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...

I think this is most unlikely (that they are on some non-conductive
metal).  At least I've never encountered one mounted like that.  Also,
it isn't terribly easy to make a "non-conductive metal" -- it is pretty
much an oxymoron, in fact.  One can INSULATE a metal by e.g. spraying it
with epoxy or enameling it, but the "metallic bond" in metals forms a
"nearly free electron" gas.

> 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.

As several people have said, aluminum or steel sheeting is fine, but
learn how to mount motherboards on it safely with risers.  If you
actually look at a motherboard mounted in most cases, you'll see that it
is sitting on somewhere between four and eight small metal
pedestal/standoffs that the screws actually screw into.  The pedestals
are locked into the case mount, which is usually steel or a composite
metal in commercial cases.

As always, using Google I easily found:

   http://www.youtube.com/watch?v=7YXro0Gs6Vc

and you can actually WATCH people mount motherboards into cases.  This
will show you pretty much what you have to do to mount motherboards onto
e.g. cookie sheets, including where you have to drill holes and mount
standoffs.

> 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...

Lots of Youtube out there.

    rgb

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

Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
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


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