Data Recovery

On this page you will find how to restore/recover information from your hard disk, cd, dvd, tape drive or flash memory, both for PC and MAC. If the damage done to your Hard disk is physical you will in most cases not be able to restore the data yourself. For this there are specialized companies whom can do the job for you.

Data recovery is the process of recovering data from primary storage media when it cannot be accessed normally. This can be 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.

Physical damage: A wide variety of failures can cause physical damage to storage media. CD ROMs and/or DVDs can have their metallic substrate or dye layer scratched off; hard disks can suffer any of several mechanical failures, such as head crash 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 recovered.

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, data recovery companies are consulted. These firms use Class 100 clean room facilities to protect the media while repairs are being made, and tools such as magnetometers are used to manually read the bits off failed magnetic media. The extracted raw bits can be used to reconstruct a disk image, which can then be mounted to have its logical damage repaired. Once that is complete, the files can be extracted from the image.

Data recovery can even be accomplished for alternate digital media such as Flash cards for digital cameras, old tape drives, etc.

Logical Damage: Far more common than physical damage is logical damage to a file system. Logical damage is primarily caused by power outages that prevent file system structures from being completely written to the storage medium, but problems with hardware (especially RAID controllers) and drivers, as well as system crashes, can have the same effect. The result is that the file system is left in an inconsistent state. This can cause a variety of problems, such as strange behavior (e.g., infinitely recurring directories, drives reporting negative amounts of free space), system crashes, or an actual loss of data. Various programs exist to correct these inconsistencies, and most operating systems come with at least a rudimentary repair tool for their native file systems. Third-party utilities are available, and some can produce superior results by recovering data even when the disk cannot be recognized by the operating system's repair utility.

Two main techniques are used by these repair programs. The first, consistency checking, involves scanning the logical structure of the disk and checking to make sure that it is consistent with its specification.

The second technique for file system repair is to assume very little about the state of the file system to be analyzed, and using any hints that any undamaged file system structures might provide, rebuild the file system from scratch.

While most logical damage can be either repaired or worked around using these two techniques, data recovery software can never guarantee that no data loss will occur. For instance, in the FAT file system, when two files claim to share the same allocation unit ("cross-linked"), data loss for one of the files is essentially guaranteed.

Finally, the entire system can be equipped with a battery backup (see Backup Battery) that may make it possible to keep the system on in such situations, or at least to give enough time to shut down properly.

GNU Free Documentation License. It uses material from the Wikipedia article "Data Recovery"