Google’s big surprise: each server has its own 12-volt battery to supply power if there’s a problem with the main source of electricity. The company also revealed for the first time that since 2005, its data centers have been composed of standard shipping containers–each with 1,160 servers and a power consumption that can reach 250 kilowatts.
Why built-in batteries?
Why is the battery approach significant? Money.
Typical data centers rely on large, centralized machines called uninterruptible power supplies (UPS)–essentially giant batteries that kick in when the main supply fails and before generators have time to kick in. Building the power supply into the server is cheaper and means costs are matched directly to the number of servers, Jai said.
“This is much cheaper than huge centralized UPS,” he said. “Therefore no wasted capacity.”
Efficiency is another financial factor. Large UPSs can reach 92 to 95 percent efficiency, meaning that a large amount of power is squandered. The server-mounted batteries do better, Jai said: “We were able to measure our actual usage to greater than 99.9 percent efficiency.”
The Google server was 3.5 inches thick–2U, or 2 rack units, in data center parlance. It had two processors, two hard drives, and eight memory slots mounted on a motherboard built by Gigabyte. Google uses x86 processors from both AMD and Intel, Jai said, and Google uses the battery design on its network equipment, too.
Efficiency is important not just because improving it cuts power consumption costs, but also because inefficiencies typically produce waste heat that requires yet more expense in cooling.
Costs add up
Google operates servers at a tremendous scale, and these costs add up quickly.
Jai has borne a lot of the burden himself. He was the only electrical engineer on the server design job from 2003 to 2005, he said. “I worked 14-hour days for two and a half years,” he said, before more employees were hired to share the work.
Google has patents on the built-in battery design, “but I think we’d be willing to license them to vendors,” Hoelzle said.
Another illustration of Google’s obsession with efficiency comes through power supply design. Power supplies convert conventional AC (alternating current–what you get from a wall socket) electricity into the DC (direct current–what you get from a battery) electricity, and typical power supplies provide computers with both 5-volt and 12-volt DC power. Google’s designs supply only 12-volt power, with the necessary conversions taking place on the motherboard.