Data Recovery

What is Data Recovery?
Data recovery may be defined as the process of retrieving data from the inaccessible or flawed parts of the storage device in a computer system. In case of the storage parts getting damaged, the data recovery process can be applied to recover secure and important data. Recovery can be from any type of storage media- primary, secondary or temporary storage devices.

Areas of application
Data recovery is generally used when there has been some damage to the storage sector physically or any logical error in the disk partitions of the storage drives. They are also used for retrieval of secure data from disks after they are deleted.

Methodology
1. Data recovery after physical damage
Physical damage to a storage device may be like the failure of the reading head in a hard drive or due to the removal of the metallic layer in a compact disk etc. In such conditions, the easiest way to compensate the damage is to replace the damaged parts with new ones. But that does not clear the consequential logical damage to the media due to the physical damage. Hence certain techniques are used for data recovery in such cases.

Hardware replacement and repair
Considering the example of a hard disk crash due to physical damage, the hardware repair is done by the immediate replacement of the damaged parts. For example, replacing the damaged circuit boards with new ones or replacing the damaged reading heads in a hard disk. It definitely clears the physical damage but may lead to some logical errors in the file system.

Virtual disks
Creating a virtual disk, popularly known as disk imaging can be very much helpful in the reconstruction of the lost data. The images can be easily converted into a usable form. Thus, logical damages can also be cleared.

2. Data recovery after logical damage
Logical damage to the file system in a computer occurs more often than physical damage to the storage media. It usually occurs due to the unexpected power failures which results in the unsaved status in the file system or incomplete rollback to the previous state of the file system. When the system is reused after such a situation, there will be an inconsistent state which may further lead to greater and severe system crashes.

Prevention
Usage of reliable file systems like ext3 can reduce the possibility of occurrence of logical damages. This is due to the design of such file systems which roll back to the previous consistent state in case of a power failure or other possibilities of logical damages. There will be loss of data from the cache memory only and not from the original file system. Another prevention mechanism is the regular de-fragmentation and disk check-up which can help in the logical and sequential arrangement of the data in the file system. Usage of a back up power system can help in the cases of power failures.

Consistency checking
The consistency check in a file system can provide with the details of errors in the file system. The presence of such errors can be subsequently dealt with the available repairing techniques. It usually browses through all the directories in a file system and can efficiently spot the bugs.

State analysis
A thorough analysis of the individual states of each of the parts of a file system or the so-called sub system can provide with the details of logical errors and can assist in the rebuilding process of the file system. This is done by analyzing the saved and unsaved states in a file system and checking the boundary conditions of the same.

Thus, the data recovery process assists in recovery of valuable data that has been lost due to physical or logical damage.