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 and saved on a reliable medium, the image can be safely analyzed for logical damage and will possibly allow much of the original file system to be reconstructed.
Corrupt partitions and file systems, media errors
In some cases, data on a hard disk 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 data recovery software such as Testdisk; software like ddrescue can 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.
Remote data recovery
Recovery experts do not always need to have physical access to the damaged hardware. When the lost data can be recovered by software techniques, they can often perform the recovery using remote access software over the Internet, LAN or other connection to the physical location of the damaged media. The process is essentially no different from what the end user could perform by themselves
Remote recovery requires a stable connection with an adequate bandwidth. However, it is not applicable where access to the hardware is required, as in cases of physical damage.
Four phases of data recovery
Usually, there are four phases when it comes to successful data recovery, though that can vary depending on the type of data corruption and recovery required.
Repair the hard disk drive
The hard drive is repaired in order to get it running in some form, or at least in a state suitable for reading the data from it. For example, if heads are bad they need to be changed; if the PCB is faulty then it needs to be fixed or replaced; if the spindle motor is bad the platters and heads should be moved to a new drive.
Image the drive to a new drive or a disk image file
When a hard disk drive fails, the importance of getting the data off the drive is the top priority. The longer a faulty drive is used, the more likely further data loss is to occur. Creating an image of the drive will ensure that there is a secondary copy of the data on another device, on which it is safe to perform testing and recovery procedures without harming the source.
Logical recovery of files, partition, MBR and file system structures
After the drive has been cloned to a new drive, it is suitable to attempt the retrieval of lost data. If the drive has failed logically, there are a number of reasons for that. Using the clone it may be possible to repair the partition table or master boot record (MBR) in order to read the file system’s data structure and retrieve stored data.
Repair damaged files that were retrieved
Data damage can be caused when, for example, a file is written to a sector on the drive that has been damaged. This is the most common cause in a failing drive, meaning that data needs to be reconstructed to become readable. Corrupted documents can be recovered by several software methods or by manually reconstructing the document using a hex editor.