Someone had a brilliant idea over there. From Ars Technica:
Microsoft updates its open server design with a battery in every box
Microsoft today announced that it was sharing a number of new designs for its cloud servers to improve efficiency and reduce the cost of management.
Last year, Microsoft joined the Open Compute Project to join Facebook and other companies to share the designs of the custom servers it uses in its large datacenters. By sharing designs and standardizing across companies, the companies involved can reduce costs and increase the range of hardware options available.
The servers are built for high density and high efficiency. The first version of the Open CloudServer specification (OCS) servers Microsoft published packed 24 server blades into a 12U chassis. Compute blades included a pair of Ivy Bridge-based Intel Xeon processors, up to 192GB RAM, one or two 10gigE ports, and up to 4 disks; storage blades packed in ten disks. The 12U units share power and networking infrastructure.
12U is 21" tall so you can fit three of these units with 6U left over for ancillary stuff (network switches, cabling, etc) in a standard 42U rack.
Some more:
The more exotic changes are from the handling of power. The power supplies of each 12U unit now include lithium ion batteries in each unit, something Microsoft calls Local Energy Storage. While lithium ion batteries are routinely used to power computers—laptops use them—that's not where Microsoft sourced the units for its servers. Instead, it's using batteries from the power tool industry. They're cheap, proven, and abundantly available.
The traditional datacenter includes large banks of lead acid batteries combined with fossil fuel-powered generators. These batteries have to be sized to power the entire datacenter for the few seconds or minutes it takes for the generators to kick in and get up to speed. This takes considerable space—as much as 25 percent of each datacenter's footprint. It's also hard to scale; the batteries have to be an appropriate size for the entire datacenter, rather than growing in proportion to the number of servers. The lead acid batteries are relatively inefficient, with about 9 percent of a datacenter's power used for charging and operating them, and being full of acid, they can be awkward to manage.
Very clever - much simpler power management and if one or more batteries fail, the rest of the server farm is still up and running. Using a commodity power tool battery is a great idea. Much cheaper than a custom design and ubiquitous. There is an engineering design philosophy: C.O.T.S. Commercial Off The Shelf - use these components and your design will be cheap and reliable.
If they wanted to be really clever, they could have the battery interface mount on a screw-in metal plate with the regulation and charging circuitry on board. This way, when the power tool company decides to retire that battery, changing over to another format will be a matter of replacing the plates. Thinking about it though, I bet the servers are replaced with the same frequency so the two can just grow old together.
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