[Beowulf] Re: Intel quad core nodes?

[Maurice Hilarius]

Daniel Pfenniger wrote:

"But while configuring a cluster remember that you can get a better
deal (=speed/cost for your application) by choosing cheaper CPUs in
larger quantities."

I disagree. Sometimes this is true, and sometimes it is not.

The CPU cost is a fractional element of the total cost. The total cost
can vary quite a bit.

Let's do a fictional example, with 60 nodes, one rack, GbE networking:

Quad core Opteron blades, in a 10 blade 8U chassis.
6 chassis per rack, 60 blades, 120 CPUs, 480 cores


1    Motherboard Opteron S1207x2/ split rail power, newer chipset,
video/GbE*2
2    AMD Opteron2347 Quad Core 1.9GHz
8    2GB DDR2 667MHz ECC REG DIMM Assuming 16GB RAM ( 2GB per core)
1    160 GB 7200rpm HDD
Total per node: $ 2,600

Blade frame/chassis/power cost per node: $300

Rack, PDU, GbE network switch, cables, etc., etc, per rack of 60 nodes: 
$6,000
Cost per node: $100

Total: $180,000

So, each node costs roughly $3,000 with 1.9GHz CPUs ( 2 per node)
Each CPUs is about $400/3000 of the cost, or 13.4%

Upgrade to:
2.0GHz: Each node is $3,200, CPU $500 15.7%
2.3GHz: Each node is $4,200, CPU $1000 23.8%
2.5GHz: Each node is $5,150, CPU $1475 28.7%

Assuming performance is pretty well linear with clock speed in your
applications.
Yes, a big assumption, but one that holds true for most,
unless you are limited by memory bandwidth or network performance..

Using the above figures, we can see that:
Upgrade from 1.9 to 2GHz: 5.3% performance gain, 6.6% cost increase.
Upgrade from 1.9 to 2.3GHz: 21.1% performance gain, 40% cost increase.
Upgrade from 1.9 to 2.5GHz: 31.5% performance gain, 72% cost increase.

When one factors power consumption and cooling the curve of
cost/performance certainly gets steeper.
But, the jump from 1.9 to 2.0 is a reasonable one.
Going from 1.9 to 2.0GHz is an example that disagrees with your statement.

Going from 1.9 to 2.3GHz it is different:
If we factor in the performance gain ( again, assuming even scaling by
simply adding nodes):
Add a second rack, add 13 more nodes, to gain 26.4% mode performance (
equiv to 1.9 vs 2.3GHz) :
2 more 10 blade chassis, 16U, more network, another rack, PDU, etc. $8,000
13 nodes @ $3,000 = $39,000
$180,000 + $47,000 = $227,000
227/180 = 26.1% cost for 21% performance gain.
It seems that the gain for more CPUs versus faster holds true for the
jump to 2.3GHz.
With Quad core Opterons it is more cost effective to add nodes versus
faster CPUs comparing 2.3GHz to 1.9GHz.

Of course you are supporting a second rack, more power, more cooling to
do so.
And, you are maintaining more nodes which is more work, more risk of
failure, etc..

-----------------------------------
Barnet Wagman wrote:
"Of course I'd rather wait for AMD's quad but that's not an option (I
doubt that they'll be readily available until next year).  So I'm
leaning towards the low cost per node solution - one quad processor
(probably a Q6600) per node."

Huh? What does "readily available" mean to you?
How many machines would you like with these?
Give me a call.



-- 
With our best regards,

//Maurice W. Hilarius         Telephone: 01-780-456-9771/
/Hard Data Ltd.                FAX:          01-780-456-9772/
/11060 - 166 Avenue         email:maurice at harddata.com/
/Edmonton, AB, Canada         http://www.harddata.com//
/     T5X 1Y3/
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