Going where few password crackers have gone before, a team of security consultants has deployed a cracking-optimized computer that’s completely submerged in mineral oil. Members say the setup offers significant cost savings compared with the same machine that uses air to stay cool.
The rig contains two AMD Radeon 6990 graphics cards, long considered a workhorse for password crackers. While the parallel processing in just one of these $800 cards can make as many as 9 billion password guesses each second (see PC3 in the graph at the bottom of this page), the performance comes at a price. GPUs run extremely hot, particularly when combined with other graphics cards, which drives up the cost of keeping them cool enough to run without burning out. The dedicated fans normally used to keep them cool also generate plenty of noise.
Employees of security consultancy KoreLogic recently deployed the password cracker at Midas Green Tech, an Austin, Texas-based data center that specializes in so-called immersion-cooled server hosting. Unlike the other air-cooled systems KoreLogic uses to test the strength of clients’ password policies, the cost of hosting it is less than $60 per month, compared to about $100 for an air-cooled system, said Rick Redman, one of the KoreLogic penetration testers who deployed the new machine.
“I’ve got this machine. It’s overheating,” Redman said. “It’s pumping out all this power. I don’t want to run it in my house because it’s too noisy and my wife complains. It’s noisy like you wouldn’t believe.” What’s more, it would require about $60 per month worth of electricity to run it at home, he estimated.
Submerging the cards in mineral oil is “quote unquote green,” Redman told Ars. “Because I don’t have to worry about air flow, I can compact them together and make them so much tighter, so I can save space and use less energy and pay less money. It’s cheaper and it’s better and it’s safer for my computer. It’s illogical for me not to do it.”
When the same machine was air-cooled, Redman said it was “overheating drastically,” even though it ran the GPUs at one of their factory-set speeds as opposed to being “overclocked to run faster.” The Radeon 6990, as opposed to many other AMD GPU models, is known to run hot.