What is Disk Cloning?

Robert Grimmick

Disk cloning, also known as disk imaging, is the practice of copying the entire contents of a hard disk or partition, including file structure and system files, for the purpose of moving or restoring the drive’s data. Cloned disks are often written to a single image file that represents the entire drive. Such a disk image can be used for many purposes including transferring data to a larger hard disk or restoring an unstable system with a clean image of the disk. Libraries, schools, and cybercafes often restore their computers with cloned disk images to easily manage and protect a large number of machines. The practice can create some problems, but many programs provide features to compensate for this.

Performing a data backup using disk cloning guards against losing information in the event of a hard drive malfunction.
Performing a data backup using disk cloning guards against losing information in the event of a hard drive malfunction.

When operating systems and back-up software copy the contents of a disk from one location to another, they often ignore some files, alter the data in some way, or fail to preserve all the attributes of files on the disk. In many cases, this is actually beneficial to the user. When backing up a folder to an external hard disk, for example, the date and time when a file was last changed may reflect the time of the last backup rather than when the original file was modified. When an exact copy of a disk needs to be made, many users may turn to disk cloning software.

Disk cloning software creates a bit-for-bit level copy of a disk, meaning that every last piece of data is preserved. The data can either be written to a second disk or saved as an image file. The image file can be used to transfer data to one or more new hard disks or reapplied to the original disk. An unstable system, for example, can be rolled back to a point where it was still functional by using a cloned disk image.

Organizations with a large number of computers can utilize disk cloning to deploy a standardized set of applications and data across many different computers. They might also use the technique to simultaneously apply updates and security patches to all their computers. In libraries, schools, and cybercafes, for example, computers are often restored from a cloned disk image on a regular basis to wipe out any viruses or other unwanted software that patrons may have downloaded. Disk cloning can also be used in conjunction with disk wiping, the practice of securely erasing a disk, to remove any personal data and return the machine to a clean slate.

Creating exact duplicates of a hard disk can have disadvantages. Computers running Microsoft® Windows® are assigned a unique Security Identifier (SID) when the operating system is first installed. Cloning a disk will copy the computer’s unique SID; if this cloned image is used on multiple computers on a network, security could be compromised. Drivers for the particular set of hardware are also copied when a disk is cloned, which can cause problems when the target system has a different setup. Some disk cloning applications provide features to overcome these problems, so potential customers should be sure to evaluate their own needs before making a purchase.

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