Data recovery is a process by which one can salvage electronic data from damaged and corrupted storage media which cannot be accessed through normal means.
There are specific recovery services being offered by these companies which specialize in hard drive recovery. You can also hire a professional and certified data recovery expert to restore the data.
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Types of media from which it has been done in the past are storage media like the HDD, the pen drive, storage tapes, CDs/DVDs, and some other optical media. The commonest of all recovery issues figure in the hard drive and Raid, where the data becomes inaccessible.
Some other problems are related to files being deleted from the resident file system. Using some techniques, the so-called deleted files can also be restored. Then of course there are the hard disk failures for which data retrieval is essential.
Any sort of its recovery, requires knowledge of why a media fails. Recovering it from defunct, failed and damaged storage media is fast becoming a major business area and there are several companies which have formed a fair business model around it.
Many firms also offer SQL data recovery which is a type of database recovery, Raid one and Mac one, especially for those Mac users.