In pictures: Take a look inside Telefonica's Madrid datacenter

Construction work on the datacenter began in November 2011, with the facility becoming operational in January last year.

Telefonica says it has so far spent around €120m on the datacenter and, once a planned expansion (see image eight) has been completed, the telco will have invested €300m.

One new addition to the datacenter is a facility that Telefonica calls the Innovation Center.

It's an area where existing and potential customers can come and see demonstrations of the technologies Telefonica is using in the datacenter, particularly around cloud computing.

Security is tight at the datacenter. As well as nearly 150 cameras dotted around the premises, access to rooms is controlled by keycard.

Doors such as the one pictured above control who can access the rooms, as well as ensuring that there are not too many people in the room at one time as the weight on the floor needs to be closely monitored.

There are also 10,000 sensors placed around the facility to monitor conditions in the building.

At the moment the Alcala datacenter contains seven rooms (six of which are operational), each covering 680 square metres and capable of holding more thn 350 racks. Around 2,000 racks are in operation at the moment.

Telefonica uses much of the space in the datacenter itself, but customers ranging from petroleum companies to supermarkets are also using the center.

The datacenter uses free cooling to keep the rooms at the optimum temperature.

During the winter, hot air generated by the equipment is recycled and mixed with cooler air to maintain the right temperature, while water vapour can also be mixed in with the air to reduce temperatures during the very hot summer months. Telefonica says free cooling is used for about 92 percent of the year.

Phase one of the Alcala datacenter was the construction of the first 25,000 square metre building, where six of the seven rooms are now operational. Eventually, Telefonica will expand the datacenter to include another four buildings, each with four rooms. The final datacenter should cover around 80,000 square metres, Telefonica says.

The cooling systems sit on the roof of the datacenter, pulling in cool air and pushing out warmer air.

The modular design and construction of the datacenter means systems controlling power and cooling are mirrored across all rooms. Telefonica says this helps with maintenance as well as construction.

Telefonica says it decided to build the datacenter in Alcala de Henares — birthplace of Don Quixote author Miguel de Cervantes — partly as a sign of confidence in Spain, and Madrid in particular, as it recovers from the crippling financial crisis.

Each room has its own diesel generator for backup in case the primary electrical supply goes down.

The modular design means each room is independent, an incident in one room will not impact any other room. Each room also has two electrical supplies, and if one goes down the other is capable of running the room on its own. This is partly what helps the datacenter achieve 99.995 percent availability, Telefonica says. PUE is around 1.4, it said.