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

Products

• VMware vCenter Server

Issue/Introduction

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

BackupManager encountered an exception.

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

Exception: Full backup not allowed during VM snapshot


     3. Example log entries in /var/log/vmware/applmgmt/backup.log

[YYYY-MM-DDTHH:MM:SS].648 [VCDBBackup:PID-XXXX] [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-XXXX] [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

     4. 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