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 Net World
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| Computers-Hardware-Data recovery | ||
| Net World Directory: Computer data recovery |
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What is data recovery? 
You may resort to data recovery, which is a process of recovering data from primary storage media when it cannot be accessed normally. The recovery is possible when you lose date 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. For simplicity we can divide data recovery into these two sections Data recovery from physical damage Many things can happen to your computer in terms of physical damage to your computer and storage media. You may drop your laptop and cause physical damage, or may cause physical damage to storage media. CD-ROMs may be damaged easily if their metallic substrate or dye layer scratched off. You hard disks can suffer any of several mechanical failures, such as head crashes and failed motors or system breakdowns. Some tapes can simply break. Physical damage may be associated with some data loss, but much of data may be recovered. Physical damage causes damage to the logical structures of the file system and may result in loss of data. Data recovery process should first deal with this logical damage before any files can be recovered. You may not be able to fix most of the problems caused by physical damage. If you try to open a hard-drive in a normal environment it can result in accumulation of dust on the surface, and this may cause further damage to the platters and complicating the recovery process. Also you may not generally have the hardware or technical knowledge required to make these sorts of repairs, so it is best to leave it to the experts if you are thinking of data recovery. The data recovery companies have special types of clean room in which the hard-drive can be opened. This protects the hard-drive from further damage while data recovery is in process. Data recovery companies use tools such as magnetometers to manually read the bits off failed magnetic media. The company dealing with your data recovery may have the capability to extracted raw bits that can be used to reconstruct a disk image, which can then be mounted to have its logical damage repaired. Once the company dealing with your data recovery completes this process, the files can be extracted from the image. It is possible to recover data from other storage media like Flash cards used for digital cameras also. Data recovery from logical damage This type of data loss is more common than the data loss resulting from physical damage, and this type of data loss results from disturbance of the normal logical architecture of the file system. Power outrage is by far the commonest cause data loss in this category. This happens because the power outrage prevents file system structures from being completely written to the storage medium. A hardware failure, or failure of the drivers may also result in loss of data due to disturbance in the logical structure of the file system. Loss of normal logical structure of the file system results in in an inconsistent state. Naturally this leads to variety of problems, such as strange behavior (e.g., infinitely recursive looping of directories, drives reporting negative amounts of free space), system crashes, or an actual loss of data. Several programs are available to correct these inconsistencies, and most of the time your operating system comes with at least a rudimentary repair tool for their native file systems. For example Linux system has a fsck utility, Apple Mac OS X has Disk Utility and Microsoft Windows provides chkdsk system. If you prefer to have a third-party utility, these are freely available, and some third party utilities can produce superior results and may be able to recover data even when the disk cannot be recognized by the operating system's repair utility. There are two basic techniques used by these repair programs. The first technique is consistency checking, and this involves scanning the normal logical structure of the disk and checking to make sure that it is consistent with its specification for the software. To give an example, in most file systems, a directory must have at least two entries: a dot (.) entry that points to itself, and a dot-dot (..) entry that points to its parent. A good file system repair program can read each of these directories and make sure that these entries exist and point to the correct directories. If they do not match, an error message can be printed and the problem can be recognized and corrected. Both chkdsk and fsck work in this way by checking on the directory structure. This strategy has major problem in the fact that if the file system is largely damaged, the consistency check may fail completely. In this case, even the repair program may crash trying to deal with the mangled input, or the repair program may simply quit because it may not recognize the drive as having a valid file system at all. A more efficient technique for data recovery is to use file system repair assuming very little about the state of the file system to be analyzed and to, using any hints that any undamaged file system structures might provide. Using this method, it may be possible to rebuild the entire file system from scratch. This technique starts with a process of scanning the entire drive and making note of all file system structures and possible file boundaries, then trying to match what was located to the specifications of a working file system. Some of the third party software that is available in the market uses this technique for data recovery. The advantage of this strategy is that it can recover data even when the logical structures are almost completely destroyed. This strategy usually does not aim at repairing the underlying file system, but merely allows for data to be extracted from it to another storage device. It is possible in most cases to have complete data recovery from logical file system damages using the two strategies mentioned above, however there is no guarantee that all the data will be recovered. To give an example, in the FAT file system, when two files are cross-linked, data loss for one of the files is essentially occurs. Newer techniques of journaling file systems, such as NTFS 5.0, ext3, and xfs, is likely to reduce the incidence of logical damage and such failures. In these cases the file systems can always be "rolled back" to a consistent state, and only data that is likely to be lost is what was in the drive's cache at the time of the system failure. It is important to include consistency checking in the scheduled system maintenance. A regular consistency-checking program can protect both against bugs in the file system software and latent incompatibilities in the design of the storage hardware. The best way to protect your data is to have consistent program for back-up of your files. A well-organized back-up program can be a lifesaver and would avoid headaches associated with data loss when your computer crashes. If you don't backup your data, a data recovery process described above may be your only option. |
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