Backup of virtual machines finishes with warnings:
Error code: 102
Message: Creating a crash-consistent snapshot of virtual machine 'XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX' because the creation of its application-consistent snapshot has failed.
Error code: 138
Message: Failed to create the virtual machine snapshot (Machine: 'XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX'; Name: 'AcronisBackup').
If you are backing up Linux virtual machines or virtual machines with dynamic disks on a Hyper-V host: application-consistent snapshot is naturally (by hypervisor itself) not supported for Linux virtual machines or virtual machines with Windows dynamic disks running on a Hyper-V host.
Make sure your Linux distribution is supported: see Supported Linux and FreeBSD virtual machines for Hyper-V on Windows Check each of the supported Linux distributions to find the one used in your environment and confirm whether "Live virtual machine backup" option applies to your Linux distribution, and make sure that Linux Integration Services (LIS) are installed inside VM.
If this warning appears during a backup of a Windows virtual machine without dynamic disks, make sure that either the latest Integration Services (for Hyper-V environment) or VMware tools (for ESX(i) environment) are installed inside the affected VM. For Windows Server 2008R2 you can use integration tools from Windows Server 2012R2.
If the issue still persists, follow Acronis Backup: virtual machine backup troubleshooting guide.
To prevent these warnings, disable the VSS for virtual machines backup option:
- Open the backup plan for editing.
- Click the gear icon to open Backup options.
- Set Volume Shadow Copy Service (VSS) for virtual machines to disabled.
What is the difference between crash-consistent and application-consistent backups of virtual machines?
A crash-consistent snapshot means that the virtual machine's data is captured at exactly the same time. Crash-consistent backups are fine and work well for the most part for if there are no database applications on the VM. When a crash-consistent backup is recovered and restored, the data is in the identical state it was in at the time of the backup.
Crash-consistent backups don't work nearly as well for database applications because they do not capture data in memory or any pending I/O operations. As such, restoring from a crash-consistent backup requires extra work, such as journaling forward, before an application can be brought back online.
In addition to providing a crash-consistent backup, application-consistent snapshots also capture all data in memory and all transactions in process. This is performed by using some type of client software co-resident with the database application to quiesce the database application, flush its memory cache, complete all its writes in order and then perform the backup. In case of Microsoft Windows and Hyper-V, this task is performed by VSS API. When the snapshot is complete, the software notifies the database application to resume. A restoration of an application-consistent backup requires no additional work to restore the database application.