Disk Cloning

Dennis Faas's picture

Disk Cloning or Disk Imaging is a category of software which copies the contents of one computer hard disk to another, or onto a secondary medium such as a DVD or CD Recordable.

A disk cloning program is most commonly used by large companies to provision new computers to install the initial package of the operating system and applications for sale, or by home computer users who wish to backup their operating systems in a healthy state. An individual user may also use disk cloning to upgrade to a new hard disk or backup an existing operating system.

To provision the hard disk of a computer without using disk cloning software, the following steps are generally required for each computer:

  • Create one or more partitions on the disk  
  • Format each partition to create a file system on it  
  • Install the operating system  
  • Install device drivers for the particular hardware  
  • Install application software 

With disk cloning, this is simplified to:

  • Install the first computer, as above.  
  • Create an image of the hard disk (optional).  
  • Revert the image to another hard disk (or save it onto secondary medium as a backup).

Disk Cloning: Operating Environment

The majority of older disk cloning programs need to be able to read even protected operating system files on the source disk, and must guarantee that the system is in a consistent state at the time of reading. It must also overwrite any operating system already present on the destination disk. To simplify these tasks, most disk cloning programs run under a version of DOS (MS-DOS, PC-DOS and DR-DOS are all used by different disk cloning manufacturers). Some disk cloning programs, notably Acronis True Image, can perform most operations without rebooting to DOS.

Running under a DOS environment does cause problems for disk cloning programs, as some devices no longer have DOS drivers available for them. Disk cloning programs often provide their own functionality for accessing tape drives, CD and DVD readers and writers, and USB and FireWire drives. They often contain their own TCP/IP stack for multicast transfer of data.

Disk Cloning: Image Transfer

The simplest method of cloning a disk is to have both the source and destination disks present in the same machine, but this is often too restrictive. Disk cloning programs can link two computers by a parallel cable, or save and load images to a network drive. As disk images tend to be very large (usually at least several hundred MB), performing several clones at a time puts excessive stress on a network. The solution is to use multicast technology. This allows a single image to be sent simultaneously to many machines without putting greater stress on the network than sending an image to a single machine.

This article is adapted from: wikiPedia.com.

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