This knowledge base article addresses the issue of VM snapshot operation failure in Vembu-VMBackup. When encountering this error message, the backup process may fail due to reasons related to snapshot file size exceeding available free space on the datastore. The article provides insights into the causes and offers solutions to resolve the problem.

VMWare backups may encounter the "VM Snapshot Operation Failed" error when the size of the snapshot file being generated surpasses the available free space on the datastore hosting the virtual machine. In such scenarios, the ESX/ESXi host aborts the operation, leading to the error message being recorded in the log. This issue can also arise when the VMware Tools within the Guest OS or the ESX/ESXi server version is outdated.

To address the VM snapshot operation failure, follow these steps:

1. Assess Disk Size and Datastore Compatibility:

1. Compare the size of the virtual machine's disks with the maximum supported VMDK size on the virtual machine's datastore.
2. If the virtual machine's disk size exceeds the supported block size of the datastore, proceed with the following options.
   

2. Adjust Virtual Machine's Configuration:

   a. Change Working Directory:

      - Move the virtual machine's working directory to a datastore with sufficient block size to accommodate the virtual machine's disk size.

      b. Relocate Configuration File:

      - Utilize Storage vMotion or cold migration to relocate the virtual machine's configuration file to an appropriate location.

3. Upgrade VMware Tools:

1. Ensure that the VMware Tools installed within the virtual machine are up-to-date.
2. An outdated VMware Tools version can lead to compatibility issues during backups.
   

4. Update VMware Tools After ESX/ESXi Host Upgrade:

Whenever an ESX/ESXi host is upgraded, it's crucial to update the VMware Tools running on the VM to match the host's version.