Data recovery is the process of salvaging data from damaged, failed, corrupted, or inaccessible secondary storage media when it cannot be accessed normally. Often the data are being salvaged from storage media formats such as hard disk drives, storage tapes, CDs, DVDs, RAID, and other electronics. Recovery may be required 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.
The most common "data recovery" issue involves an operating system (OS) failure (typically on a single disk, single-partition, single OS system), where the goal is to simply copy all wanted files to another disk.
This can be easily accomplished with a Live CD, most of which provide a means to 1) mount the system drive, 2) mount and backup disk or media drives, and 3) move the files from the system to the backup with a file manager or optical disc authoring software. Further, such cases can be mitigated by disk partitioning and consistently moving valuable data files to a different partition from the replaceable OS system files.
The second type involves a disk level failure such as a compromised file system, disk partition, or a hard disk failure in each of which the data cannot be easily read. Depending on the case, solutions involve repairing the file system, partition table or MBR, or hard disk data recovery
techniques ranging from software based recovery of corrupted data to hardware replacement on a physically damaged disk. These last two typically indicate the permanent failure of the disk, thus "recovery" means sufficient repair for a one time recovery of files. A third type involves the process of retrieving files that have been deleted from a storage media. Although there is some confusion as to the term, the term "data recovery" may be used to refer to such cases in the context of forensic purposes or spying.
Every hard drive runs a type of File System, a method by which the operating system installed can organise data and free space in a way that it can be written to and read from. Each physical disk can be split up into many partitions, each partition can in turn appear as a logical drive (addressed C:, D:, E: etc...). This guide will only deal with the 2 primary partition types used for Windows Operating Systems - FAT16/32 and NTFS.
NTFS (NT File System) is now the most common File System, and it is used by Windows NT/XP. FAT-32 is used by Windows 98 and upwards, where as FAT 16 was used by DOS/3.1/95. The most recent operating systems are backwards compatible with older file systems, and can read/write to secondary disks based on the older file system.Both file systems organise the way the data is stored by using a Master Boot Record (MBR) and a Partition Table. These are found in the first sector of the drive, and determine how the disk structure is organised and instructs the computer which partition to boot from.