If your Mac is failing to boot or your hard disk is making ominous clicking noises, an option is to send your hard disk to a data recovery specialist. We visited Kroll Ontrack at their facilities in Epsom, Surrey, to see how they do it, to discover just what can go wrong with these chunks of hardware that we trust our businesses and precious family memories to, and to help us understand what we can all do to guard ourselves against future data loss.

What's in a hard disk?

Inside the case of a hard disk, platters – made of metal or glass – are coated in a thin layer of magnetic material. A read-write head floats tens of nanometers above the surface of the platter, flicking back and forth to read from the data tracks recorded on the platters as a series of ones and zeros.

These tracks are tightly packed – Seagate has drives that cram over 52GB into a square inch, though most commercially available disks store less.

If all this sounds precarious to you, you’d be right. If things can go wrong, they will go wrong - and that’s a lesson many of us have had to learn the hard way.

Finding a solution

Up till now, there wasn’t an official solution. While there are many data recovery firms, those that speak Mac are rare, and though Kroll Ontrack has been working with Apple for years, the lack of a verified provider meant that people working for Apple or on its behalf couldn’t recommend Kroll Ontrack.

Now that the company is verified, having your hard disk repaired, which involves taking it out of your Mac, doesn’t invalidate your warranty.

The process of fixing a hard disk will be strangely familiar to anyone who’s watched medical dramas. The first step is like triage – getting a story from the customer to try to build up a picture of what has gone wrong, then working out what to do.

Later, technicians can try to match up this story with what they find with the drive itself. This description also helps the technicians figure out whether the problem lies with the physical disk mechanism itself or with the data.

Robert Winter, Kroll Ontrack’s chief engineer tells us that of the drives the company sees, 70% suffer from physical problems and 30% are so-called logical problems, everything from corrupt directories to accidentally reformatted drives.

The clean room

The first priority is to get an image of the drive, by cloning its contents onto the company’s 100TB RAID systems. If the drive is physically damaged – worn components, physical trauma – it goes into the clean room.

This stage isn’t about ‘fixing’ the drive – it’s not worth risking your data to a patched-up drive that has already failed. “We just want to get it running long enough to make that image,” Winter tells us.

Once the problem has been diagnosed, Kroll Ontrack will consult with the customer to see what can be done and how much it will cost.

“The average data recovery cost we see here is about £800,” says Phil Bridge, Kroll Ontrack UK’s MD, “but that’s not to say we don’t have cheaper options; our photo recovery service, for example, costs £299.”

Before visiting the clean room, we had visions of Spielbergian white rooms with decontamination chambers, but if fact all that is not really necessary. Each bench has a huge air filter above it, sure, but we could wander in without first donning an Outbreak-style suit.