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Understanding Clones

A clone is a copy of an existing virtual machine. The existing virtual machine is called the parent of the clone. When the cloning operation is complete, the clone is a separate virtual machine — though it may share virtual disks with the parent virtual machine: see Full and Linked Clones).

  • Changes made to a clone do not affect the parent virtual machine. Changes made to the parent virtual machine do not appear in a clone.
  • A clone's MAC address and UUID are different from those of the parent virtual machine.
  • If you want to save the current state of the virtual machine, so you can revert to that state in case you make a mistake, take a snapshot. If you want to make a copy of a virtual machine for separate use, create a clone.

    Why Make a Clone?

    Installing a guest operating system and applications can be time consuming. With clones, you can make many copies of a virtual machine from a single installation and configuration process.

    Clones are useful when you must deploy many identical virtual machines to a group. For example:

  • An MIS department can clone a virtual machine for each employee, with a suite of preconfigured office applications.
  • A virtual machine can be configured with a complete development environment and then cloned repeatedly as a baseline configuration for software testing.
  • A teacher can clone a virtual machine for each student, with all the lessons and labs required for the term.
  • With clones you can conveniently make complete copies of a virtual machine, without browsing a host file system or worrying if you have located all the configuration files.

    Full and Linked Clones

    There are two types of clone:

  • A full clone is an independent copy of a virtual machine that shares nothing with the parent virtual machine after the cloning operation. Ongoing operation of a full clone is entirely separate from the parent virtual machine.
  • A linked clone is a copy of a virtual machine that shares virtual disks with the parent virtual machine in an ongoing manner. This conserves disk space, and allows multiple virtual machines to use the same software installation.
  • Full Clones

    A full clone is an independent virtual machine, with no need to access or maintain an ongoing connection to the parent virtual machine. Because a full clone does not share virtual disks with the parent virtual machine, full clones generally perform better than linked clones. However, full clones take longer to create than linked clones. Creating a full clone can take several minutes if the files involved are large.

    Linked Clones

    A linked clone is made from a snapshot of the parent. (See Understanding Snapshots.) All files available on the parent at the moment of the snapshot continue to remain available to the linked clone. Ongoing changes to the virtual disk of the parent do not affect the linked clone, and changes to the disk of the linked clone do not affect the parent.

    A linked clone must access the parent. Without access to the parent, a linked clone is disabled. See Linked Clones and Access to the Parent Virtual Machine

    Linked clones are created swiftly, so you can easily create a unique virtual machine for each task you have. You can also easily share a virtual machine with other users by storing the virtual machine on your local network, where other users can quickly make a linked clone. This facilitates collaboration: for example, a support team can reproduce a bug in a virtual machine, and an engineer can quickly make a linked clone of that virtual machine to work on the bug.

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