Specifications

CHAPTER 5 Preserving the State of a Virtual Machine
153
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 on page 150.
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 on page 156 and Removing the Snapshot on page 157.
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 in
the VMware GSX Server Administration Guide. 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.