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A snapshot preserves the state and data of a virtual machine at a specific point in time. You can create a snapshot before upgrading or installing a patch.
The best time to take a snapshot is when no applications in the virtual machine are communicating with other computers. The potential for problems is greatest if the virtual machine is communicating with another computer. For example, if you take a snapshot while the virtual machine is downloading a file from a server on the network, the virtual machine continues downloading the file and communicating its progress to the server. If you revert to the snapshot, communications between the virtual machine and the server are confused and the file transfer fails.
![]() | CAUTION |
Snapshot operations can adversely affect service. Before performing a snapshot operation, you must stop the application that is running on the virtual machine or place the application out-of-service. When the snapshot operation is complete, start or bring the application back into service. |
Snapshots can:
Consume large amounts of data resources.
Increase CPU loads on the host.
Affect performance.
Affect service.
To prevent adverse behaviors, consider the following recommendations when using the Snapshot feature:
Do not rely on VMware snapshots as a robust backup and recovery method. Snapshots are not backups. The snapshot file is only a change log of the original virtual disk.
Do not run a virtual machine from a snapshot. Do not use a single snapshot for more than 24 to 72 hours.
Take the snapshot, make the changes to the virtual machine, and delete or commit the snapshot after you verify the virtual machine is working properly. These actions prevent snapshots from growing so large as to cause issues when deleting or committing the snapshots to the original virtual machine disks.
When taking a snapshot, do not save the memory of the virtual machine. The time that the host takes to write the memory to the disk is relative to the amount of memory that the virtual machine is configured to use. Saving the memory can add several minutes to the time taken to complete the operation. If the snapshot is active, saving memory can make calls appear to be active or in progress and can cause confusion to the user. To create a clean snapshot image from which to boot, do the following when you create a snapshot:
In the Take Virtual Machine Snapshot window, clear the Snapshot the virtual machine’s memory check box.
Select the Quiesce guest file system (Needs VMware Tools installed) check box to ensure that all write instructions to the disks are complete. You have a better chance of creating a clean snapshot image from which to boot.
If you are going to use snapshots for a long time, you must consolidate the snapshot files regularly to improve performance and reduce disk usage. Before merging the snapshot delta disks back into the base disk of the virtual machine, you must first delete stored snapshots.
![]() | Note |
If a consolidation failure occurs, end-users can use the actual Consolidate option without opening a service request with VMware. If a commit or delete operation does not merge the snapshot deltas into the base disk of the virtual machine, the system displays a warning on the user interface. |
Title | Link |
Best practices for virtual machine snapshots in the VMware environment | Best Practices for virtual machine snapshots in the VMware environment |
Understanding virtual machine snapshots in VMware ESXi and ESX | Understanding virtual machine snapshots in VMware ESXi and ESX |
Working with snapshots | Working with snapshots |
Configuring VMware vCenter Server to send alarms when virtual machines are running from snapshots | Send alarms when virtual machines are running from snapshots |
Consolidating snapshots in vSphere 5.x | Consolidating snapshots in vSphere 5.x |