VMWare Server Tip: Discard Changes To Virtual Machines Without OS Reinstall


vmwarelogo.jpgWhen testing Software, drivers, hotfixes, or any kind of updates, Virtual Machines (VM) can make life a lot easier, especially for System Administrators. With free virtualization tools available such as VMware Virtual Server, the average consumer can now take advantage of using this technology that once belong in the Datacenter.

Having the ability to test on a virtual machine, knowing if something goes wrong and you cannot recover or reboot, just requires a reinstall of the OS in the VM. But why rebuild, when you can easily revert back to the original state with Snapshots.


Snapshots allow you to preserve the state of the virtual machine so you can return to the same state repeatedly. You can take a snapshot while a virtual machine is powered on, powered off, or suspended. Once a snapshot has been created, you can test any changes made to the OS, and reboot or shutdown as normal. If anything goes wrong during testing, you can revert back to the snapshot to the state the VM was before you made changes.

If testing was successful, you can discard the snapshot and use the OS with the changes, or create a new snapshot and continue testing. A real time saver while eliminating the need to reinstall the OS.

When taking snapshots, the entire state of the virtual machine is captured at the time you take the snapshot. This includes, the state of all the VM disks, contents of the VM memory, and the virtual machine settings. When you revert to the snapshot, you return all these items to the state at the time you took the snapshot.

One item to keep in mind with snapshots is disk space. A snapshot creates a separate file that is used to write any changes made to the VM. As changes are made, the snapshot file will grow until either the changes are committed to the VM main disk files, or the snapshot is removed.

Creating Snapshots

You can easily create a snapshot from the console by right clicking on the Virtual Machine and selecting Take Snapshot. Once it is created, and you have tested, you can then Revert to Snapshot to discard changes or Remove the Snapshot.


Settings can also be specified whether the machine is powered on or powered off. If the virtual machine has no snapshot, you can disable the snapshot feature by selecting Disable snapshots. If you have a snapshot and want to disable the snapshot feature, first go to the console window and choose Snapshot/Remove Snapshot, then from the virtual machine settings editor, select Disable snapshots. To lock the snapshot so no new snapshot can be taken, select Lock this snapshot.


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July 17, 2007

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