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--- title: VM Snapshot extension using VMs restore points description: VM Snapshot extension using VMs restore points author: aarthiv ms.author: aarthiv ms.service: azure-virtual-machines ms.subservice: recovery ms.topic: how-to ms.date: 11/2/2023 ms.custom: template-how-to # Customer intent: As a cloud administrator, I want to utilize VM snapshot extensions for application-consistent restore points, so that I can ensure the integrity of my applications during backup operations. --- # VMSnapshot extension --- Application-consistent restore points capture Virtual Machine data in a state that guarantees application integrity at the time of the snapshot. To achieve this, Azure coordinates with applications running on the Virtual Machine before taking the snapshot: - **Windows**: The **VMSnapshot Windows** extension triggers the Volume Shadow Copy Service (VSS) to quiesce application writes. - **Linux**: The **VMSnapshot Linux** extension runs pre- and post-scripts to flush and resume application I/O. When you request an application-consistent restore point, Azure automatically installs the VMSnapshot extension on the Virtual Machine if it isn't already present. The extension updates automatically no manual management is required. > [!IMPORTANT] > Azure begins creating a restore point only after **all extensions on the Virtual Machine**, including VMSnapshot, has finished provisioning. Monitor extension provisioning state before expecting restore point creation to succeed. To confirm the extension is installed and in a **Provisioned** state, check **Virtual Machine > Extensions + applications** in the Azure portal, or run: ```azurecli az vm extension show \ --resource-group <resourceGroupName> \ --vm-name <vmName> \ --name VMSnapshot ``` ## Extension logs Use the following paths to access VMSnapshot extension logs directly on the Virtual Machine: | OS | Log path | |---|---| | Windows | `C:\WindowsAzure\Logs\Plugins\Microsoft.Azure.RecoveryServices.VMSnapshot` | | Linux | `/var/log/azure/Microsoft.Azure.RecoveryServices.VMSnapshotLinux/extension.log` | ## Troubleshooting Communication issues between the Virtual Machine agent and the VMSnapshot extension cause most restore point failures. Start troubleshooting with [Troubleshoot restore point failures](restore-point-troubleshooting.md). ### VSS writer failures (Windows) When a VSS writer fails, Azure can't take an application-consistent snapshot and falls back to a file system-consistent restore point. This fallback applies for the **next three attempts**, regardless of the configured restore point schedule. From the **fourth attempt onward**, Azure resumes attempting application-consistent restore points. To resolve VSS writer failures, see [Troubleshoot VSS writer issues](/azure/backup/backup-azure-vms-troubleshoot#extensionfailedvsswriterinbadstate---snapshot-operation-failed-because-vss-writers-were-in-a-bad-state). > [!WARNING] > Don't manually delete the VMSnapshot extension. Deleting it breaks subsequent application-consistent restore point creation until the extension is reinstalled and provisioned again. ## Next steps [Create a Virtual machine restore point](create-restore-points.md)