NetSPI Blog

GPU Cracking: Rebuilding the Box

Karl Fosaaen
April 27th, 2015

A little over two years ago, we built our first GPU cracking box. At the time, there was pretty limited information on what people were doing to build a decent cracking box, especially if you were trying to do so without breaking the bank. As with any piece of technology, things go out of date, things get upgraded, and documentation needs to get updated. Since it’s now two years since I wrote about our first system , I figured it was time to write an update to show what we’re actually using for cracking hardware now.

The Case

We currently have two cracking systems, Development and Production. Our development system is seated in a really nice (and relatively cheap) case that we picked up from The big downside of this case is that we can’t immediately buy another one. The group making the case had recently switched to a Kickstarter model (we were one of the only backers), but they secured outside funding for the cases and are now building more. As soon as they have them ready, we’re planning on picking up another one.


Our production system is currently housed in a much lower-tech case… Three Milkcrates. As you can see, we’ve graduated from server shelving to an arguably crazier option. After seeing a number of Bitcoin miners using the milkcrate method for cases, we moved our cards over. This has actually worked quite well. The only issue that we’ve run into (outside of noise) is high temperatures on some of the cards. We’ve been able to keep the heat issues away by manually setting the fan speeds on all of the cards to 100%.


*Update (5/19/15): We actually got another rack-mount case for our production system. Goodbye milk crates.


The Motherboard

One of the big changes that we were happy to see over the last two years was the move by hardware manufacturers to embrace Bitcoin miners (even though most have moved off of GPU mining). ASRock now makes a Bitcoin specific motherboard (H81 PRO BTC) that is specifically geared towards running multiple GPUs. With six PCI-E slots, it’s a very inexpensive ($65) choice for creating a cracking box. Five of the slots are PCI-E 1x slots (and mounted pretty closely together), so you will need to use risers to attach your cards.

The Risers/Extenders

Another Bitcoin focused product that we’ve been using are the USB 3.0 PCI-E risers  (or extenders). These little devices allow you to put a PCI-E 16x card into a PCI-E 1x slot. The card then attaches to the motherboard with a USB cable. Basically, these extend your PCI-E slots using USB cables. These are much cleaner and more reliable than the ribbon riser cables we started using.

The Cards

I will say that I really like the newer cards (R9 290) that we are currently running. They have decent cracking rates and I really haven’t had too many issues with them so far. The biggest issue has been heat. This can mostly be mitigated by having decent airflow around the case and setting the fan speeds on your cards to the max. The fan speeds can be set using the aticonfig command  (pre-R series cards) or od6config for newer cards. One of the biggest pains that I’ve dealt with on our systems is getting all the fans set correctly for all the cards, specifically when you have a mix of older and newer cards. For simplicity’s sake, I would recommend going with one card model for your cracking box. The newer cards are nice, but if you can find someone trying to offload some older 7950s, I would recommend buying those.

The Power Supplies

Our recommendations on power supplies haven’t changed. Only running one to three cards? You will probably be fine with one power supply. Going any higher and you will want two. Shoot for higher wattage power supplies (800+) and get a Y-Splitter.

CPU/RAM/Hard Drive

All of these can be generic. It doesn’t hurt to max these out, but they don’t really impact cracking performance. If you’re going to throw money around, throw it at your cards.

Here’s a pretty general parts and pricing list if you want to build your own.

Component Model Est. Price
Case 6 GPU Rackmount Server Case $495
Motherboard ASRock Motherboard H81 PRO BTC $64
Risers (6) PCI-E 1X To 16X USB 3.0 Riser Card $24
GPUs (6) XFX Black Edition R9 290 $1,884
Power Supply (2) CORSAIR AX1200i 1200W $618
Power-Splitter Dual PSU Adapter Cable $9
RAM 8 GB – Any Brand $50
CPU Intel Celeron G1820 Dual-Core (2.7GHz) $45
HDD 1 TB – Any Brand $50
Total $3,239

If you have any questions or better parts recommendations, feel free to leave a comment below.

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16 Comments on "GPU Cracking: Rebuilding the Box"

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What about the energy bill : can you tell us what you pay for what consumption ? does the cracking box constantly run or do you turn it on for few hours ?


What kind of speeds are you getting on the new cards?


Any tips on other cases, as the one mentioned is not available anymore AFAIK?


Where did the HDD go in the case?

Hi Karl, I’ve just started building my own box follwing your useful blog ,so thanks a lot for the handy info first of all. I’m half-way through at the moment, so only have one AX1200i Platinum PSU with 3 x XFX Black Edition Radeon R9 Cards and a H81 PRO BTC motherboard. I just have a Dual core CPU and 8GB of RAM. All of the cards are using powered USB 3.0 risers. The rig seems to work fine with only two of the cards, but as soon as I add the third card it wont boot up at all?… Read more »

Hi, Do you recommend using 2 Titan X ?


Hi Karl,

I have started building this rig as a project but after ordering all the parts apart from GPUs
I was advised that these GPUs have 4GB VRAM each so I should have at least 24GB of host RAM. I was also told that I should have at least an i5 CPU. My question to you is why have you used a low end CPU & RAM for this rig? and can I run this rig successfully with your setup and later upgrade my RAM & CPU.



Hi Karl,
What do you suggest to collect computer part , according to the high table. The following as well :
– costs $ 15000 to be
– the use of new parts
– considered cooling of amd GPU

Igor Rymyk

Hello there

What is the temperatures on GPU on that case ?
Are they not going two hot?


But you forgot to mention how fast it can crack a password between 8-11 or 8-16 alpha numberic upper lower case characters. using crunch + cuda/oclhashcat.. ?? let me know the answer please