[Beowulf] newbie's dilemma

Robert G. Brown rgb at phy.duke.edu
Wed Mar 1 15:09:59 PST 2006

On Tue, 28 Feb 2006, Don R. Baker wrote:

> for 8 years, but consider myself to still be a beginner.  I have a room
> with 4, 15 amp circuits and a 20 000 btu air conditioning unit installed
> that I can use for the next 2 years, but after that I may need to find
> another home for the system.

Let's see.  20KBTU is a bit more than 1.5 tons of AC, call it the
ability to remove 5800 Watts total.  4 x 15 x 120 is is 7200 Watts peak,
or about 5000 Watts RMS.  In my opinion this is going to leave you a bit
light on AC if you run the circuits fully loaded, and don't forget warm
bodies (60 W) and built in light bulbs etc. on other circuits (maybe
several hundred W more).  You have to not only remove the heat as fast
as it comes in but get ahead some, correct for heat that infiltrates
through the walls, and get the room temperature down below 20C (68 F) if
at all possible.  15-16C is more like it -- cold enough to just be

If you limit what you run per circuit to roughly 1000 Watts, that is
4000 watts and gives you a bit of margin.  Or get a bigger AC -- a 2 ton
AC is still pretty cheap and would probably manage fully loaded
circuits.  Just a thought.

> My dilemma is that for my budget I can buy one of the following
> solutions:
> Solution #1
> A custom built "personal cluster" with 8 dual core processors either
> Xeons or Opterons (16 cores and 16 GB of memory) with all the software
> installed, read to go.
> Solution #2
> I can buy 16 workstations, each with Dual Core Athlon X64 4400+
> processors (32 cores and 32 GB of memory) upon which I will probably
> install either Warewulf or Oscar.
> Solution #3
> I can buy 32 HP or Dell "mass market" desktops running dual core chips
> (64 cores and 64 GB memory) upon which I will probably install either
> Warewulf or Oscar.  (Note that I read the discussion this past November
> on "cheap PCs this christmas")
> Obviously, I get more computing power in the last two solutions, but at
> what cost in terms of time and upkeep?  Once the system is up and
> running I can dedicate about 5 hours per week, and probably no more, and
> CAD$ ~500 per year for maintenance.

I personally would reject #3 out of hand, unless you buy three year
onsite service contracts on the Dells (spending nodes as required).
Dell doesn't do Opterons, I don't think, as well.  HPs ditto.

Solutions #1 or #2 are both reasonable, although I'm not sure where your
numbers are coming from.  It might be more helpful if you gave us your
budget and your software constraints (e.g. how much memory per CPU or
core do you need).  I'm assuming embarrassingly parallel MC (which is
what I do) so the network is basically irrelevant.

> Do any of you have some sage advice?  Have any of you used a "personal
> cluster"?  Any thoughts you may have will be very much appreciated.
> Thank you all for your time.

Sure, a bunch of us (myself included) have personal clusters, although
yours is going to be mine -- I never have more than about 10 nodes
because at that point my house starts to melt in the summertime (and the
nodes start to cost roughly $1000/year just to run).  Remember, power
costs ballpark of $1/watt/year to heat AND remove the heat (within a
factor of two) so if you DO fill your room to capacity with 4000 watts
running 24x7, plan to spend around $4000/year just to run it and keep it

> Wishing you the best from a cool Montreal,

Although there is that -- I suppose in the wintertime you could just
open a window and snow-cool it... but that at most knocks it down to
$3000, because most of the money is for the power, not the cooling:-).

>From this point of view getting fewer, faster nodes (e.g. 8 dual-dual
core processor from e.g. Penguin or ASL (32 processor cores) is likely
to be a net savings in power, in money PAYING for power, high quality
nodes are less likely to break, and less of your time doing both soft
and hard maintenance.  I'd really try to keep your system count down for
home clusters as they can eat enough time and money to destroy personal
relationships with loved ones...

They don't have to be preinstalled with linux, though.  Oh, they may BE
preinstalled (often with SuSE) but I'd advise reinstalling Centos or FC
(see archives for pros and cons of choice).  That way you get an
indefinite free update stream and full yum-ability.  SuSE does yum
(thanks to Joe Landman of this list, who might ALSO sell you prebuilt
nodes) but it ain't necessarily pretty...


> Don

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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