Data recovery after a hard drive failure
is the process of extracting data from damaged, failed, corrupted, or
inaccessible primary storage media when it cannot be accessed normally. Often
the data are being salvaged from storage media formats such as hard disk drive,
storage tapes, CDs, DVDs, RAID, and other electronics. 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. 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.Data recovery after a hard drive failure
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.
Despite this, there are many accounts of users getting a bad disk going long enough to pull their data off, often via slightly bizarre tricks. These include making the drive cold (in the freezer) or spinning it manually on the ground, both actions being used to unstick a jammed platter. Most data recovery professionals recommend against the use of tricks such as these, as they can cause additional physical damage to the drive if done improperly (and in many cases, even when done properly).
Data recovery techniques
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, but there may still be logical damage. A specialized disk imaging procedure is used to recover every readable bit from the surface. Once this image is acquired, the image can be analyzed for logical damage and will possibly allow for much of the original file system to be reconstructed.
