Taking Snapshots

The snapshot feature is most useful when you want to preserve the state of the virtual machine so you can return to the same state repeatedly.

To simply save the current state of your virtual machine, then pick up work later with the virtual machine in the same state it was when you stopped, suspend the virtual machine. For details, see Suspending and Resuming Virtual Machines.

You can take a snapshot of a virtual machine at any time and revert to that snapshot at any time. If the virtual machine is located on a Linux host, you should not take a snapshot while you are suspending the virtual machine; wait until the snapshot is completely saved, then take the snapshot.

You can take a snapshot while a virtual machine is powered on, powered off or suspended. A snapshot preserves the virtual machine just as it was when you took the snapshot — the state of the data on all the virtual machine's disks and whether the virtual machine was powered on, powered off or suspended.

Once you take a snapshot, the virtual machine starts saving any changes to the virtual machine to one or more redo-log files. The redo log can grow quite large as data is written to it. Be aware of how much disk space these logs consume. If you need to free up some disk space, you can remove a virtual machine's snapshot, which writes all the changes in the redo log to the virtual disk. For more information, see Snapshots and a Virtual Machine's Hard Disks and Removing the Snapshot.

Note: If you are using a legacy virtual machine — for example, a virtual machine created under GSX Server 2 and not upgraded to use the new GSX Server 3 virtual hardware — you must power off the virtual machine before taking a snapshot. For information on upgrading the virtual hardware, see Upgrading VMware GSX Server. You also must power off the virtual machine before taking a snapshot if the virtual machine has multiple disks in different disk modes — for example, if you have a special purpose configuration that requires you to use an independent disk.

When you revert to a snapshot, you discard all changes made to the virtual machine since you took the snapshot. This includes any data written to the virtual disk and any changes to the virtual machine's configuration.

Similarly, if you take a snapshot of a virtual machine then modify the virtual machine's configuration, any changes you make to the configuration are not reflected in the snapshot. You need to take a new snapshot.

You can take a new snapshot at any time. When you do so, you replace the previous snapshot. You can have only one active snapshot at a time.

Note: Taking a new snapshot when the virtual machine is powered off and a snapshot already exists can take a long time, as the original snapshot needs to be removed. While you are taking a new snapshot, other consoles may not be able to connect to the server host and the users trying to connect may see an error that the VMware Registration Service (vmware-serverd) is not running.