In this second part i will cover some aspects on different types of data recovery. Of course, it is not an easy topic, as explanations are usually more technical than in other issues. As stated in wikipedia, there are two different techniques by which specialists can recover your lost data. Although data recovery is usually successfully performed, there is no way to be sure that the whole data lost will be recovered. It is computers, not magic. That is why having the best qualified person to do the job is always the first point you have to think when hiring this service. The two techniques cited can be called “consistency checking” and “Zero-knowledge analysis” (see en.wikipedia.org). in the first case, “Consistency checking involves scanning the logical structure of the disk and checking to make sure that it is consistent with its specification. For instance, in most file systems, a directory must have at least two entries: a dot (.) entry that points to itself, and a dot-dot (..) entry that points to its parent”. In other words, each directory and file have there own and unique identification, as there can’t be files or directories with the same name. What the data recovery program does is, in the first place, read each directory to detect that every entry is corectly assigned and named. The two examples cited are Chkdsk (Checkdisk), and fsck (File system check). There is one main drawback with this firs technique: if the file system is damaged, the program for data recovery may crash once and once again without being able to work out the problem. As stated in the cited website, “If chkdsk finds a data file to be out of place or unexplainable, it may delete the file without asking”. In this case, Checkdisk may have solved your problem, but it might also deleted a file that was important to you.

The second technique, Zero-knowledge analysis, is more interesting, as it tries to restore the damaged file from structures analyzed and detected in undamaged files from your operative system. Of course, this strategy implies a much slower process, as all the system is scanned to list all damaged files and to study the structures of all undamaged files, so as to start from that point to rebuild the structure of the file that was damaged. This strategy, even though it is slower, allows to recover data that you might have thought to be lost, and put it in another storage location.

So as you see, it is not magic: there are programs and algoritms involved, there is a process in which technology and professionals are involved. But what about overwritten data? Can it be recovered? Well, this is a question that stills puzzles all the brains in the field of technology and PCs. Until now, it has been proved impossible, as no examples from the practice could be presented. There was a project, from Peter Gutmann, that is referred by Wikipedia, in which scanning transmission electron microscopy is apparently involved, but no proof has made it possible to think he is right.

Data recovery, then, is not a magic method and it may not always be entirely successful.