File-Based backup in vCenter VAMI UI fails with "Full backup not allowed during VM snapshot"

Products

• VMware vCenter Server

Issue/Introduction

• Attempts to perform a file-based backup using the vCenter Server VAMI UI fail with the following error message:

BackupManager encountered an exception.

• Upon reviewing the backup.log file located at /var/log/vmware/applmgmt on the vCenter, the following error entries are observed:

Exception: Full backup not allowed during VM snapshot


• Example log entries in vCenter /var/log/vmware/applmgmt/backup.log

[YYYY-MM-DDTHH:MM:SS].648 [VCDBBackup:PID-####] [VCDB::BackupVCDB:VCDB.py:2060] ERROR: Encounter error during backup VCDB. Traceback (most recent call last): File "/usr/lib/applmgmt/backup_restore/py/vmware/appliance/backup_restore/components/VCDB.py", line 1939, in BackupVCDB raise Exception('Full backup not allowed during VM snapshot') Exception: Full backup not allowed during VM snapshot
[YYYY-MM-DDTHH:MM:SS].746 [MainProcess:PID-####] [BackupManager::Cleanup:BackupManager.py:406] ERROR: Failed to clean up backup child processes. Exception: Hit exception inside process VCDBBackup: Full backup not allowed during VM snapshot

 

• The issue persists even when the "Stats" and "Tasks" options are selected during the backup process.

Environment

• VMware vCenter Server 7.x
• VMware vCenter Server 8.x 

Cause

This issue occurs due to the presence of a zero-byte file named backupMarker.txt located in the /etc/vmware/ directory on the vCenter Server Appliance.

This file acts as a marker, indicating that a VM snapshot operation is in progress. When this file exists, vCenter prevents any full file-based backup operations to avoid conflicts or corruption during concurrent snapshot-based backups.

The file may remain in place under the following conditions:

• A previous backup operation was interrupted or failed

• VM migration activities (e.g., vMotion) were performed recently

• Third-party backup software created snapshots but did not clean them up properly

Resolution

To resolve the issue and allow file-based backups to proceed, follow these steps:

1. Access the vCenter Server Appliance using SSH.
   
   
2. Navigate to the VMware configuration directory:

cd /etc/vmware

     3. Verify the presence of the snapshot marker file:

ls -l backupMarker.txt

     4. If the file exists, delete the file by running:

rm /etc/vmware/backupMarker.txt

     5. Reattempt the file-based backup using the VAMI UI.

     6. Monitor future backup operations to ensure that backups complete successfully. 

Additional Information

• The backupMarker.txt file is used internally to prevent multiple simultaneous backup operations. Its presence simulates an active snapshot, which blocks any new full backup attempts.

• The error message "Full backup not allowed during VM snapshot" indicates that vCenter detects an active snapshot state, even if no snapshots are visible in the inventory.

• This issue is typically environmental and can result from backup software behavior or incomplete cleanup after system events.

For more information on identifying active VM snapshots, refer to:
Finding and listing virtual machine snapshots