[Beowulf] Re: Beowulf of bare motherboards

Andrew Piskorski atp at piskorski.com
Sat Oct 23 13:03:56 PDT 2004

I recently experimented with running multiple motherboards off a
single power supply.  This is pretty easy now, because you can buy Y
power cables now - no soldering necessary:

"ZIPPY Power Cable Splitter: ATX 20 pin to Two ATX 20 pin for ATX
Power Supplies", $11 for one; 8 of these cost me $8.49 each shipped:


I wanted to find out how many nodes I could power from a single
supply, and I happened to have 4 different power supplies on hand for
testing.  In all cases, I plugged the supply into my Kill-a-Watt,
attached 3 of the above y-cables to the supply, and simply varied the
number of motherboards plugged into those 4 connectors.

The 4 nodes in question are all Ebay specials, configured like so:

- Motherboard:  ECS P4VXMS
- 1 Pentium 4 CPU, socket 423, 256 KB cache, 400 FSB;
  speed GHz:  1.3, 1.4, 1.5, 1.7
- 1 stick RAM, 512 MB PC133 CL3
- 1 AGP graphics card installed, various models.
- 1 Panaflo fan (80 mm, 12 V, 0.1 A) blowing on the CPU heat exchanger.
- THAT'S IT.  (No hard drives, etc.)

Below, the reported Watts is simply the approximate maximum W value I
saw on the Kill-a-Watt as the nodes booted.  The Powe Factor is the
lowest and/or most typical PF reported by the Kill-a-Watt:

ThermalTake Purepower HPC-420-302 DF, Active PFC, 420 W
  $53 +$7 from newegg.com
2 nodes, 175 W, PF 0.98,  $34.25 per node
3 nodes, would not boot, [$25.67 per node]
4 nodes, would not boot, [$21.38 per node]

MGE SuperCharger, 600W
  $48 +$7 from newegg.com
2 nodes, 175 W, PF 0.66,  $31.75 per node
3 nodes, 255 W, PF 0.67,  $24.00 per node
4 nodes, would not boot, [$20.13 per node]

Enermax EG301P-VB, 300 W
  $31.50 +$7 from newegg.com
2 nodes, 155 W, PF 0.67,  $23.50 per node
3 nodes, 226 W, PF 0.68,  $18.50 per node
4 nodes, would not boot, [$16.00 per node]

Sparkle FSP250-61GT, 250 W
  Ancient, used to power my old AMD K6-II 380 MHz dektop.
2 nodes, 170 W, PF 0.64
3 nodes, 241 W, PF 0.64
4 nodes, 331 W, PF 0.65

Note that I didn't actually RUN anything on the nodes at all, I just
plugged in a monitor and verified that they got through the POST ok
and attempted to boot.  (They attempt to PXE boot, but I don't yet
have anything set up for them to PXE boot FROM.)

Newegg used to advertise the MGE 600 W supply above as having active
PFC, (which is why I bought it), but nothing on the supply itself says
anything about PFC, and the Kill-a-Watt results definitely show that
it doesn't have PFC.

I find it interesting that the smallest, oldest, and probably cheapest
supply is the only one that successfully booted all 4 nodes at once.
Perhaps it is running out of spec, and simply lacks the circuitry to
shut down in such cases?

These motherboards each beep once when they boot, and the beeps seemed
to all come very close together with some supplies, and further apart
with others.  I didn't pay attention to which supplies did this, but
this is probably why the Kill-a-Watt seemed to show lower peak Watts
for the Enermax supply?

Unfortunately I didn't have any el-cheap $12 (plus shipping) supplies
to test.  Particularly since these nodes are diskless, those might
actually work just fine.  Newegg is also now selling the slightly
larger 480 W ThermalTake active PFC supply for about the same price as
the 420 W supply above, which would be worth trying if you really want

Andrew Piskorski <atp at piskorski.com>

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