The hard disk drive in your computer is the place where the data is stored, and the data is at its most current. So, if it fails and there is not a current backup then it can be a very serious problem.
Why will a disk fail?
Data on a hard drive is stored on a circular platter that spins at anything from 5400 rpm to 15,000 rpm., with a read/write head mounted on an arm that positions it across the platter to access data. This head “floats” very close to the surface by dint of an aerodynamic effect, add to this movement and proximity the potential for heat generation and there is suddenly a lot that can go wrong.
This is when the head touches the surface of the platter whilst it is spinning, this could be the result of an impact or a mechanical failure within the HDA (HDA is the Head Disk Assembly which comprises the head/platter combination).
It is not too difficult to imaging the consequence of such contact, in the worst cases it can strip away the entire recorded surface of the platter leaving just the base material, usually glass.
Hard disk drives “hide” any instance of media failure to maintain a perfectly readable disk, and prevent operating system problems as the result of unreadable sectors. What they do is maintain a set of spare sectors, and when failures occur they reallocate data to one of these spares.
There can come a point where the spares are all used up and the errors begin. Normally the disk is in quite a sever state of failure by now and if the disk is kept working the problems will rapidly multiply.
Hard drives are controlled by circuitry that is susceptible to damage from electrostatic discharge or electrical surge. If a component is on the brink of failing then quite a minor electrical “blip” will push it over the edge.
The complexity with a hard drive is that there is code and information stored within memory devices on the drive controller and this is created when the drive is first formatted, so just replacing the electronics will not help.
Alignment failure and head failure.
If any of the read heads within the drive fail, and can no longer turn the magnetic signal going past into something that can be decoded by the drive electronics then again the disk drive has failed. Even if the heads have not failed but mechanical wear means that positioning to the correct place to find data is just not happening, then you can have lots of perfectly well recorded data but not means of accessing it.
Platter rotation has to be nice and smooth, any undue vibration can cause positional problems. Following an impact, or just after prolonged use, the bearings that allow the platter to rotate can crumble and seize. The drive cannot spin the platter and no data can be read.
Sometimes the problem lies not with the disk but with the person or system that is using it. The disappearance of a partition or files might actually be user error or the result of an application error, the disk might still be working perfectly well.
Hard Drive Data Recovery
This is the general term for a collection of techniques for getting the data of a failed device and finding a way of returning it in a usable form. This can range from quite a straightforward process, to a highly complex on, and in the worst case an impossible task.
It is tempting to depend on the general reliability combined with a belief that in the unlikely event of a failure a data recovery services can help. Many firms cite 95% + success rates so why worry? First, the only statistic that matters is whether your disk can be recovered from, 500 other disks might have been recovered from 100%, but if yours has crashed beyond redemption then your data has gone.
Second, even a low cost data recovery will cost more than a 500GB USB disk, so why risk everything to save virtually nothing?
Hard Drive Data Recovery is an option, sometimes a business or marriage saver, but by taking a bit of care it can be an option that you do not need.