Building a mini cluster – Part 3: One power supply to feed them all…

After going over the hardware selection in my previous post, we still need to get power to the servers…

The power system is going to be a difficult part of this build… As I wrote earlier, I am not a DYI person and I’ve been on the receiving end of enough electric shocks that, frankly, electricity scares me. But there is no way I can use discrete power supplies for every motherboard because:

  • every power supply would need to be (slightly) over-dimensioned
  • every power supply is an AC/DC converter which is wasteful
  • it would be too expensive
  • it would require too much space

 

Can I use a PC power supply?

My first idea is to simply use a regular, beefy computer power supply and figure out a way to use it to power multiple servers. Sadly though, a PC power supply has a specific cabling setup that is ideal for one PC, but that not easily lends itself to what I need.

My boards only take one power feed between 9V and 19V. Basically, this means that all the 5V leads are pretty much useless and the 20V leads are too hot. Possibly 20V might still be usable, but these boards are usually fed using 12V power bricks. 20V will, if the boards do not blow up, significantly shorten their expected lifespan.

Now people have used regular power supplies and are still doing so, but the modification work seems way too much work to me and the end result is not exactly pretty, in my opinion.

http://web2.murraystate.edu/andy.batts/ps/powersupply.htm

 

Using a “generic” power supply

So I need to go way out of my comfort zone and get a simple power supply that takes 220V AC and gives 12V DC out. Some internet searching leeds me to the MeanWell site. Apart from the friendly name, I can find a lot of good reviews of their products and they seem to have a very wide product range. After reading and comparing a lot of product data sheets, I decide on the MeanWell RSP-500-12 AC/DC 500W 12V/41.7A.

 

  • it is very small, only 230x127x40.50 mm
  • it gives the 12V I require on three output terminals
  • I figure each board will need about 1 Amp, so 41.7 Amp should be ample to feed the boards
  • I expect to only need about 250W power, so a 500W power supply should definitely be enough
  • it has active PFC (Power Factor Correction)

The three 12V output terminals should be plenty since I have pretty much decided to make two cabinets of six motherboards each. Looking at the motherboard, I expect a six board housing to be a nice little cube. The power supply will power two (and in future maybe three) compute “pods” so it needs to be external in it’s own little case.Great! Looks like I am going to be making three cases now… :s

I do need to make a custom power harness to cable all the boards from one power supply though, so next step is to look for DC jack connectors, cables and something that allows me to split one cable coming from the power supply into multiple cables going to the motherboards.

 

This leads me further down the mysteries of electronics… Since I have not touched a soldering iron since high-school, I try very hard to avoid anything that requires that particular skill. I am very happy to find these cables with connectors to plug into the motherboards

 

I still have some speaker cable laying around which look like the same thickness as these cables. That should be good enough to carry the DC current. I do need to get an extra cable to carry the 220V to the power supply.
I am still looking for a way to connect the leads from the motherboards to the leads coming from the power supply…

Networking

 

Apart from the power sub system, I also order two 8 port gigabit switches to put in each compute pod. Having an 8 port switch per six motherboards leaves me two free ethernet ports so I can daisy-chain the compute pods and have a lead to the external network. Since these also need to be powered from the power supply, I need to find switches that run on 12V. It turns out to be quite difficult to deduce what kind of power supplies are used on switches, but after some searching I find the Netgear GS108 switches that should work fine. They have some good reviews and are not too expensive. The only bad thing about them is that the power connector is smaller than those for the motherboards and I cannot find any cables with attached connectors. So I will, reluctantly, have to get get loose connectors. Ah well, I guess it was going to be unavoidable to do some soldering anyway… To be sure I need the smaller connectors, I’ll hold off ordering them until I have the switches, though.

Miscellaneous

Additional purchases include some cable shoes to put on the 220V cable to the power supply, a crimping tool for the shoes and 56 spacers which I think are a good idea to make motherboard “stacks”.

Total spend so far

I am going to put this in a table now. I’m also splitting the costs in a few categories to have a good idea of where the money is going.

Sadly, adding the switches and the power supply did break my 2.000,00 EUR budget for the server hardware. But I do think I won’t be adding anything else to that category so I can live with it.

 

Shop PartCode Description Amount Price
CarTFT.Com Mitac PD10BI Rev 1 Intel Bay Trail Celeron J1900 4×2.42Ghz 12 72.70
CarTFT.Com Shipping 1 13.53
SiComputers.nl CT51264BF160BJ Crucial PC3-12800 4GB 24 23.50
SiComputers.nl WD5000LPVX Western Digital Blue 500GB SATA 6Gb/s 12 42.50
SiComputers.nl Shipping 1 5.85
Routercenter.nl GS108GE Netgear GS108 8-Poorts Gigabit Switch Duo Pack 1 73.00
eoo-bv.nl DA5M3X40 Afstandsbus 1x binnen-1x buiten M3 40mm 56 0.27
eoo-bv.nl Shipping 1 7.00
Conrad.nl 1293106 MeanWell RSP-500-12 AC/DC 500W 12V/41.7A 1 141.14
Conrad.nl 1082735 DC aansluitkabel tweelingkabel 13 2.30
Conrad.nl 735440 Ringkabelschoen blauw 1.5 – 2.5mm M3.5 8 0.63
Conrad.nl 735327 Ringkabelschoen rood 0.5 – 1.0mm M3.5 8 0.52
Conrad.nl 844519 Krimptang 1 6.29
Conrad.nl 1218498 NK 103 S-500 5mm Zwart 1 9.99
Hardware €2,160.54 95.71%
Case €15.12 0.67%
Cables €49.09 2.17%
Tools €6.29 0.28%
Shipping €26.38 1.17%
Total €2,257.42
I have started to design the housing cabinets. I expect the next post to cover that.
Jhon Masschelein

Author: Jhon Masschelein

Tackler of advanced Cloud and Hadoop challenges in a world of open-source technologies. – Impossible is merely a matter of time and effort. –

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