Ever think about where your stuff is stored? Perhaps you use Dropbox. Or Mobile Me. Or Gmail or Hotmail. Although the talk is always of storing things "in the cloud", everything still has to be kept on a physical drive somewhere.
And that storage produces a lot of heat, takes a lot power and needs an awful lot of processor cores. And then there's redundancy – if one server or even a whole data centre was to go down, there's always a backup.
So we went to Germany to visit some of Europe's largest data centres, owned by web host 1&1. The company is huge – especially in its home country – delivering five billion non-spam emails a month and having 11 million domain names on its books. The company has 9.44 million paid-for contracts and 26.6 million free accounts. Just over a million of its customers are in the UK.
It all started with just one Windows desktop PC in Karlsruhe, Germany and now the company has over 70,000 servers at several different data centres in Europe and the US. All have used green electricity since 2008.
The first of two data centres we visited was at Baden Airpark, an ominous property at a former air force base that remains a monument to the Cold War (albeit one that's now a sparsely populated business park).
The base was formerly occupied by French and Canadian air forces before it was finally closed in 1993, and the runway is now a small provincial airport, as demonstrated by the Ryanair planes flying in.
The data centre building is a former engine workshop with huge two-foot thick metal doors. These house a giant airlock that you feel like you might never get out of. We climbed the stairs and entered one of the server rooms. The noise and heat hits you while the rows of strip lights flash on automatically.
Each server is identified by its own QR code. There are occasional gaps or unconnected cables where servers need to be changed or repaired.
Believe it or not, this whole facility is unmanned and any maintenance requests flash up at 1&1's control centre in Karlsruhe. Each room also has comprehensive power management and cabinets dedicated to keeping the temperature constant.
The Airpark building has 2,000 square metres of floorspace with 30,000 servers. There's nothing else here apart from the racks and a roof full of cooling equipment. The noise from the coolers is the only indication from outside that something sensitive lies within.
There are a whole lotta cables, too.
The second data centre we visit – Karlsruhe Brauerboulevard – is in a much more urban setting, and looks more like a standard office building – albeit with some fairly comprehensive cooling on the 1,000 square metre roof and 25,000 servers in the basement.
This setup cost £15 million and boasts 11 separate computer rooms with 660 racks. It uses 8MW of power – the city it's in consumes just 361MW as a whole.
Everything is built with redundancy in mind, so there are two complete cooling systems to remove the hot air. There are eight cold water sets and 61 air circulating coolers.
If the power should fail, massive battery rooms can power the servers for up to 20 minutes.
In reality, it takes mere seconds for the diesel engines on the roof to power up and take over. As it is, the engines look virtually unused – because they are. In fact, they've only come on-stream once, two years ago, and for a very "short period of time". Five of these massive 39 tonne units also sit atop the roof.
Again, there are redundant engines on standby and, should there be a major power problem for days on end, 1&1 has arrangements with diesel fuel suppliers as a contingency. The building also has early fire detection with gas extinguishing systems so that the servers are not harmed if a small fire is detected.
The building also has incredible security. Not only are there 190 cameras, but access controls at all points and a man trap to gain access to the server rooms themselves.
Before TechRadar visited, we had to provide our weight to 1&1 so we wouldn't get caught in the mantrap.
Soon, though, these data centres will be dwarfed by a new sibling. 1&1 is also building a data centre (see below) with space for over 100,000 servers at Hanau. Work started two years ago in a building that was a nuclear fuel factory to produce mixed oxide rods from enriched uranium and plutonium, but it never became operational. It'll be huge.
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Dan (Twitter, Google+) is TechRadar's Former Deputy Editor and is now in charge at our sister site T3.com. Covering all things computing, internet and mobile he's a seasoned regular at major tech shows such as CES, IFA and Mobile World Congress. Dan has also been a tech expert for many outlets including BBC Radio 4, 5Live and the World Service, The Sun and ITV News.