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Understanding snapshots and AutoProtect in VMware Fusion (1014509)

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Purpose

This article guides you through understanding and using snapshots in VMware Fusion. It explains common uses for snapshots and the operations that are available.

Resolution

A snapshot is a record of all of the changes made to a virtual machine since it was taken. Taking a snapshot creates a new virtual disk file, and this virtual disk is dependent on the first virtual disk because the snapshot shows changes in relation to that first virtual disk. Without the first virtual disk, the snapshot is useless as it shows that changes were made, but not what was changed.

A second (or later) snapshots, taken after the first snapshot, works in the same way. The first (or previous) snapshot stops recording changes, and the new snapshot begins recording changes.

For more details on how snapshots work, VMware recommends these two posts from our Team Fusion blog:
AutoProtect is a way to automate the taking of snapshots. With AutoProtect enabled, you can configure how often snapshots will be taken (based on time when the virtual machine is running), and how many AutoProtect snapshots to keep. Each snapshot will take up at least as much disk space as the RAM you have allocated to the virtual machine, as well as the space required for each change you make before the next snapshot is taken.

Here are a few key points about snapshots and AutoProtect.

A snapshot:
  • Is not meant to be a method of backup and recovery. If the files containing a virtual machine are lost, its snapshot files are also lost. For information on backups, see Best practices for virtual machine backup (programs and data) in VMware Fusion (1013628).
  • Negatively impacts the performance of a virtual machine. This is based on how long it has been in place and how much the virtual machine and its guest operating system have changed since the time it was taken. VMware does not recommend running production virtual machines off snapshots on a permanent basis.
  • Can take up as much disk space as the virtual machine itself. If multiple snapshots are possible, the amount of disk space used increases with the number of snapshots in place.
  • Represents the state of a virtual machine at the time it was taken.
  • Includes the files and memory state of a virtual machine's guest operating system.
  • Includes the settings and configuration of a virtual machine and its virtual hardware.
  • Is stored as a set of files in the same directory as other files that comprise a virtual machine.
  • Should be taken when testing something with unknown or potentially harmful effects.
AutoProtect:
  • Automatically takes snapshots at set intervals based on the up-time of the virtual machine.
  • Is not considered a backup strategy.
  • Should only be used in testing environments.
Description of snapshot operations:

Snapshot OperationEffect
Take SnapshotThe current state of the virtual machine and its guest operating system is captured.
Revert to Snapshot/ Restore SnapshotThe state of the virtual machine and its guest operating system reverts back to what it was when the snapshot was taken.

Warning: All data added/changed after the snapshot is permanently lost.
Delete SnapshotThe current state of the virtual machine and its guest operating system is kept and the existing snapshot is deleted.

Warning: All data associated with the deleted snapshot is kept, but the ability to revert to this point in time is lost.

Additional Information

See Also

Update History

08/12/2010 - Added more information about snapshots and AutoProtect; Added links to blog posts. 08/23/2012 - Added Fusion 5.x to Products 08/30/2013 - Added Fusion 6.x to Products

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