Ghost imaging, often called cloning, is a software-driven data backup process that copies the contents of a computer hard disk in a single compressed file or set of files, referred to as an image. The ghost image copies the entire contents to another server or hard disk for storage, including configuration information and applications. The software also converts a ghost image back to its original form when needed. On personal computers (PCs), ghost imaging is used to back up everything on the hard disk, often while reinstalling an operating system (OS).
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The purpose of the ghost image is to allow the cloning of the system onto other systems, or to enable a quick restore of a system. Ghost imaging is often used to quickly set up blocks of notebooks, tablets or servers. It enables migration from one disk or PC to another, for example, to transfer from a hard disk to a solid-state drive.
How ghost imaging works
Ghost imaging usually creates a disk image of the software on a computer, including systems settings and details. That image allows quick installation of a new copy. The ghost image is often compressed to save space and speed up transfers to the target system, and it may be encrypted for security. A typical cloning setup has a number of alternative images in a library.
Ghost imaging tools can make hundreds of PCs as exact copies. A master machine is built, and its hard disk is imaged to a file. Then, all the other machines have that image applied, followed by a customization process that gives the installed OS its own identity.
Pros and cons of ghost imaging
Ghost imaging is much faster than installing each machine separately, especially if it involves installing many applications.
There are different types of ghost images, depending on use case. For example, a data center supporting many mobile devices and desktops will need a tool focused on updating mobiles in batches, as well as individual restores. A cloud cluster will likely only use the imaging tools that are part of the cloud software stack. High-performance computing setups use ghosting to create images across hundreds or thousands of servers.
Ghosting can save hours of setup time compared with loading programs from scratch, and it reduces errors in the process.
However, updates are not incremental. When the new image replaces the OS on the destination, local user data or customization is lost.
Images are tied tightly to one hardware platform. If an organization has many different target-system types, creating and managing images is difficult.
Support can also be a challenge. For example, Microsoft does not support image-based cloning of installed Windows systems.
History of ghost imaging
New Zealand entrepreneur Murray Haszard developed "ghost," an acronym for "general hardware-oriented system transfer," in the mid-1990s. Symantec Corp. acquired the backup and disk cloning technology in 1998 and integrated it into its Norton product line, now called the Symantec Ghost Solution Suite.
At the time, Ghost was the only easily available product that could take an image of an entire hard drive. Ghost could either save the image as a file on another drive, or transfer the image to another hard drive, making the new drive an exact copy of the old drive.
Examples of ghost imaging software and alternatives
Symantec Ghost Solution Suite 3.2, released in 2017, includes disk image capture and deployment; Windows, Apple and Linux support; a streamlined, no-cost database option for small environments; and XFS file system support.
Alternatives to Symantec Ghost imaging software include:
- Acronis True Image, targeting the Windows market;
- Open source tools such as Clonezilla, dd and Partimage;
- EaseUS Todo Backup;
- StorageCraft drive imaging tools; and
- NetApp for rapid image distribution.
In addition, OpenStack cloud software and major cloud service providers maintain image cloning tools and libraries. Cloud imaging tools fulfill a similar function within a cloud's cluster, but are limited to the specific cloud type.
Microsoft and Apple provide tools for creating clones that are a mixture of an image manager and a ghosting tool.
SmartDeploy takes a different approach, cloning to a virtual machine it creates on the target system, which allows a platform-independent ghosting process.
Ghost imaging and disaster recovery
Having a loadable image for all or part of the data involved makes disaster recovery easier. For example, recovering a crashed desktop to a new PC typically involves loading an image containing the OS, with settings, followed by an image containing user applications. The same is true at the server level, except that settings for networking and security will be added.
The gear is restored to a point in time, with the ghosting utility determining how frequently data is added to the clone image. Proper use of networked storage as a replica point for current data can limit data loss to virtually nothing.
Ghost imaging vs. disk cloning
Disk cloning is the act of copying the contents of a computer's hard drive. The contents are typically saved as a disk image file and transferred to a storage medium, such as another computer's hard drive.
Disk cloning is used for system recovery, as a public computer's reboot and refreshing, and for recreating a system configuration on a new computer. The term can be used interchangeably with ghost imaging.
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