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Computer Crashes: Hardware and Software Failures

Hardware Malfunctions:

Electrical discharge or power spike causing the spinning platters in the disk interior to crash

Head or media crash wherein the read and write heads of the spinning platters directly collide with each other causing the disk to corrupt

Controller failure

A hardware failure can be easily spotted when the disk stops spinning and there is a whirring or clicking sound emanating from the computer. CD-ROMs can have their metallic substrate or dye layer scratched causing massive head crashes. On the other hand, tapes may simply break due to head disk failure where the BIOS of the used computer no longer sees or auto detects the inputted storage media device.

It is recommended that when storage media suffers mechanical or hardware crashes, data recovery experts be called to investigate the crash and restore lost data. Users are advised not to experiment on crashed hardware media to retrieve data. Users do not have the skill or the facilities to open the storage media to remove the bad sector from the rest of the device – nor can the user image or duplicate the entire data stored on the drive. All these functions can be performed adequately by the data recovery experts who make ample use of scanners, precision instruments, data imaging methodology and clean room technology to deal with the storage media crash problem.

Logical or Software Errors: These internal application errors include:

Interior disk corruption due to bad or damaged disk diagnostic or repair tools

Failed disk configurations

Damaged backups

A user becomes aware of a software problem when the software application does not load and there is a similar message on the computer screen. A logical error generally occurs when power outages prevent file system structures from being completely written to the storage medium. Logical errors usually leave the file system in an inconsistent state causing a variety of problems including infinitely recursing directories, drives reporting negative amounts of free space, system crashes or an actual loss of data. Various diverse programs exist to correct these inconsistencies -- Linux is equipped with the fsck utility, Mac OS X has Disk Utility and Microsoft Windows provides chkdsk. Third-party utilities such as The Coroners Toolkit and The Sleuth Kit are also available in the market. Generally, these can retrieve data even when the disk cannot be recognized by the operating system's repair utility. Utilities such as TestDisk have also proven useful for reconstructing corrupted partition tables.

Prevention Methods

Hardware Repair: These preventiion methods include removing a damaged PCB i.e. printed circuit board and replacing it with a matching PCB from a healthy drive. This method usually entails the movement of a microchip from the original board to the replacement drive. It also includes changing of the original damaged read/ write head assembly with matching parts from a healthy drive after the removal of the hard disk platters from the original damaged drive and installing them into a healthy drive.

Disk Imaging: Data recovery experts use the method of data imaging where the entire drive or any other storage media is duplicated on to another similar drive. This ensures that the saved data is also not lost when the drive is opened by the experts. The extracted raw image can be used to reconstruct usable data after the drive has been repaired. The files may be in usable form although recovery is often incomplete. Data imaging tools include ILook Iximager, DCFLdd v1.3.4-1 and DCFLdd v1.3.4-1.

Consistency Checking: This method involves scanning the logical structure of the disk and checking to ensure that it is consistent with its specification. Usually, in file systems a directory has at least two entries: a dot (.) entry that points to itself, and a dot-dot (..) entry pointing to its parent entry. A file system repair program can read each directory ensuring the existence of each directory and it eventually points in the correct direction. An error message is printed and the problem is corrected when this does not happen. The consistency checking tools of chkdsk and fsck work in this fashion.

Zero-knowledge Analysis: The second technique is built on zero assumption of the state of the file system to be analyzed. The method also includes the usage of any hints that any undamaged file system structures might provide to rebuild the file system from scratch. The technique involves scanning the entire drive and noting down all file system structures and possible file boundaries and then trying to match the file location with the file specification.

By: James Walsh

Article Source: http://www.myaddirectory.com

James Walsh is a freelance writer and copy editor. If you are concerned about data loss and would like more information on Data Recovery see www.fields-data-recovery.co.uk

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