Data recovery is the process of salvaging data from damaged, failed, corrupted, or inaccessible secondary storage media when it cannot be accessed normally. Often the data are being salvaged from storage media formats such as hard disk drives, storage tapes, CDs, DVDs, RAID, and other electronics. Recovery may be required due to physical damage to the storage device or logical damage to the file system that prevents it from being mounted by the host operating system. Although there is some confusion as to the term, data recovery can also be the process of retrieving and securing deleted information from a storage media for forensic purposes or spying.

Recovering data after physical damage

A wide variety of failures can cause physical damage to storage media. CD-ROMs can have their metallic substrate or dye layer scratched off; hard disks can suffer any of several mechanical failures, such as head crashes and failed motors; tapes can simply break. Physical damage always causes at least some data loss, and in many cases the logical structures of the file system are damaged as well. This causes logical damage that must be dealt with before any files can be salvaged from the failed media.

Most physical damage cannot be repaired by end users. For example, opening a hard disk in a normal environment can allow dust to settle on the surface, causing further damage to the platters and complicating the recovery process. Furthermore, end users generally do not have the hardware or technical expertise required to make these repairs; therefore, costly data recovery companies are consulted to salvage the data. These firms often use "Class 100" * cleanroom facilities to protect the media while repairs are being made. * Class 100 has now been replaced by the new ISO standards in both the US and Worldwide. any data recovery firm without a pass certificate of IS0-5 or lower will not be accepted by hard drive manufacturers for warranty purposes moreover their chances of a successful rebuild will be reduced because of the higher incidence of airborn dust which can be caught between the heads and the platter resulting in futher head crashes and data loss.