Im looking at setting up some processing nodes for my project and am testing using a node of just MoBo + memory and the network hookup (and a flash drive to boot Liniux). I'd like to save the price of power supplies and wonder if I can splice in a second set of all the required MoBo power cables to run a second (maybe a third) MoBo. I didnt think the power supplies are controlled by the MoBo, but am concerned that powerup surges will disrupt a previously started MoBo. You can get pretty good deals on MoBo + middle range CPUs + memory with it costing about the same as a middle quality power supply (with more watts than the chopped down node actually needs). I'll make the enclosure so that aspect along with cooling is immaterial.

Quote: Original post by wodinoneeye
...
I didnt think the power supplies are controlled by the MoBo, ...

Err, well ... The "power on" button is usually connected to the MoBo but not (directly) to the supply unit. The OS is usually able to switch off the supply as the last action of the shutdown procedure. A wake-on-lan enabled network card is able to power on the computer ... Look e.g. here for the PS_ON signal pin (assuming you're speaking of ATX MoBos).

Quote: Original post by haegarr

Quote: Original post by wodinoneeye
...
I didnt think the power supplies are controlled by the MoBo, ...

Err, well ... The "power on" button is usually connected to the MoBo but not (directly) to the supply unit. The OS is usually able to switch off the supply as the last action of the shutdown procedure. A wake-on-lan enabled network card is able to power on the computer ... Look e.g. here for the PS_ON signal pin (assuming you're speaking of ATX MoBos).

I cound handle that pin 14 line seperately to keep the power supply on.

All the rest dont look like any problem.

Still Im concerned about surges compromising another board that is already on (I dont have any harddrives so at least there isnt that power draw).

I wouldnt need to cut the power too closely, one 500W si\upply could probably power 3 Mobos still with alot of power left over.

Later I would be moving to higher power processors (like quads) but I would then just have to make allowances with the power supply selections.

You could very easily overdraw current from the power supply. Best case scenerio you'll end up with two unstable motherboards, as its difficult to balance two independent systems running off of the same power source. That and splicing will make the power supply attempt to deliver the same rock solid voltage across now half as much resistance, doing calculations, that equals double the current drawn when both are drawing their max instantaneously.

Quote: Original post by Jarrod1937
You could very easily overdraw current from the power supply. Best case scenerio you'll end up with two unstable motherboards, as its difficult to balance two independent systems running off of the same power source. That and splicing will make the power supply attempt to deliver the same rock solid voltage across now half as much resistance, doing calculations, that equals double the current drawn when both are drawing their max instantaneously.

Isnt a similar case when the disk drive/cd starts up (maybe the Caps on the Mobos these days -- but then the other Mobos caps help make up the difference.)

I suppose I could get away with starting all of them simultaneously (assuming crash&burn isnt part of the SOP ...)

I could still have sufficient overcapacity allowance to prevent most of the effect (the dinky power supplies ar still at a premium price these days and the cheap ~300W tend to be bulk, one larger unit could easily handle 4 Mobos for the price of 2 standard power supplies.

Quote: Original post by wodinoneeye

Quote: Original post by Jarrod1937
You could very easily overdraw current from the power supply. Best case scenerio you'll end up with two unstable motherboards, as its difficult to balance two independent systems running off of the same power source. That and splicing will make the power supply attempt to deliver the same rock solid voltage across now half as much resistance, doing calculations, that equals double the current drawn when both are drawing their max instantaneously.

Isnt a similar case when the disk drive/cd starts up (maybe the Caps on the Mobos these days -- but then the other Mobos caps help make up the difference.)

I suppose I could get away with starting all of them simultaneously (assuming crash&burn isnt part of the SOP ...)

I could still have sufficient overcapacity allowance to prevent most of the effect (the dinky power supplies ar still at a premium price these days and the cheap ~300W tend to be bulk, one larger unit could easily handle 4 Mobos for the price of 2 standard power supplies.

No, its not similar, you'll notice the atx mobo power connections are really running off of their own line. As for the capacitors on mobos, they are usually there as noise filters, usually for higher frequency noise. They usually will not help too much with voltage drops.
I suppose you can try it and see what happens. When running both, if they even startup, you can use an oscilloscope and see how much the voltage is dropping (use an oscilloscope over an voltmeter, as the voltmeter may not show the true nature of the fluctuations).

Get multi-socket motherboards instead. Or get a $19 200W power supply for each of the motherboards. Or do both. Either choice means that you don't have to worry about patching fan sense and power switch leads.
A dual-socket Xeon motherboard with two quad-core Xeons on it will deliver more compute power per dollar than most doubled-up single-board set-ups -- and it will be easier to administer, too. And if you need more than 8 cores, then just put multiple of them in a rack enclosure.

If you want real compute power density, I would recommend a blade server of some sort, such as the Cray CX1, which by the way runs Windows and can be had with high-end graphics cards, so I suppose it could also play Quake. OK, maybe only if you're filthy rich, but still :-)

Quote: Original post by hplus0603
Get multi-socket motherboards instead. Or get a $19 200W power supply for each of the motherboards. Or do both. Either choice means that you don't have to worry about patching fan sense and power switch leads.
A dual-socket Xeon motherboard with two quad-core Xeons on it will deliver more compute power per dollar than most doubled-up single-board set-ups -- and it will be easier to administer, too. And if you need more than 8 cores, then just put multiple of them in a rack enclosure.

If you want real compute power density, I would recommend a blade server of some sort, such as the Cray CX1, which by the way runs Windows and can be had with high-end graphics cards, so I suppose it could also play Quake. OK, maybe only if you're filthy rich, but still :-)

I considered one power supply each. The miniATX (small ones) have a premium price. The cheap ones are bulky and I always wonder about the quality.
Blade servers have a high price also (and a bit of overkill for what Im doing nearterm).
The 2 socket server mobos similarly have premium prices and single quads might be my eventual solution (with doubled up power supplies or one each) but I still have reservations about how well the memory can keep the CPUs fed on a quad (the multi-core discussion elsewhere...) even the 12MB caches some have (Q9450) might not help with the very random ai data access.

The idea of the beowulf cluster made from medium to lower end consumer grade hardware (Q6600 is 'middle' now) was what I was aiming at. (with mass production discounts that kind of rig at one time had the highest MIPS/$)

Mobo + CPU (core 2 duo or quad )
Power (each or shared)
Memory ~2GB (look at how cheap PC6400 is now...)
Flash drive for the 'disk' -- for OS load (& a little persistant data)
Network GigaLAN (maybe 2)
Linux
No Case -- a homebuilt rack of shelves


It likely will turn out that ganged power will be more trouble than its worth.

You could go the dc to dc power supply route. You could buy a few of the picopsu from mini-box.com and then hook them up to a quality dc power supply, something like Iota Engineering's DLS-55 http://www.iotaengineering.com/12vdc.htm . The picopsu run around $55 and the DLS-55 is around $155. You would be interested in the PicoPSU-120-WI-25 wide input 120 watt model since the Iota psu pump out 13.6vdc. In this config you could run 6 pico supplies . You could even put a deep cycle battery between them for a buffer/battery backup. The efficiency of this system would be quite high ~80% . The iota psu is about the size of two atx psu , and the picopsu are slightly larger than a 24pin atx MB connector. This is about as small a volume you could get to supply power to six motherboards.

-john w