Data recovery is recovering data from damaged, failed, corrupted, or inaccessible storage media when it cannot be accessed. Data is being recovered from storage media such as internal or external hard drives, solid state drives (SSD), USB flash drive, storage tapes, CDs, DVDs, RAID, and other electronics. Recovery may be needed due to physical damage to the storage device or logical damage to the file system.
The most common data recovery is an operating system failure, accidental damage typically on a single disk, single partition, single OS system in which the files are copied to another disk.
Another example is a disk level failure, such as a compromised file system or disk partition, or a hard disk failure. In any of these cases, the data cannot be easily read.
Also with files that have been deleted from the drive. Typically, the contents of deleted files are not removed immediately from the drive; instead, references to them in the directory structure are removed, and the space they were in is now available for overwriting. The original file contents remain in a number of disconnected fragments, and may be recoverable.
Different types of failures can cause physical damage to the drives. Physical damage always causes some data loss, and in many cases the logical structures of the file system are damaged as well. Any logical damage must be fixed before files can be recovered from the failed media.
Most physical damage cannot be repaired by the average consumer. Opening a hard drive in a normal environment can allow airborne dust to settle on the platters causing further damage and compromise the recovery process. Clients generally do not have the hardware or technical expertise required to make these repairs. Data recovery companies are often employed to salvage important data with the more reputable ones using class 100 dust & static free cleanrooms.
Recovering data from physically damaged hardware can involve multiple techniques. Some damage can be repaired by replacing parts in the hard disk. This alone may make the disk usable, in order to extract the data but there may still be logical damage.
In some cases, data on a hard drive can be unreadable due to damage to the partition table or file system, or to intermittent media errors. In the majority of these cases, at least a portion of the original data can be recovered by repairing the damaged partition table or file system using specialized software. The software can rescue the image media despite intermittent errors, and image raw data when there is partition table or file system damage. This type of data recovery can be performed by people without expertise in drive hardware, as it requires no special physical equipment or access to platters. Sometimes data can be recovered using relatively simple methods and tools; more serious cases can require expert intervention, particularly if parts of files are irrecoverable. Data carving is the recovery of parts of damaged files using knowledge of their structure.