vCenter Server Backup Fails with "BackupManager encountered an exception" Due to SMB Connection Limits

Products

• VMware vCenter Server

Issue/Introduction

When attempting to perform backups of vCenter Server to an SMB share, the backup process fails with the error message "BackupManager encountered an exception. See logs for details." The backup log shows NT_STATUS_SHARING_VIOLATION errors during the cleanup phase.

• Backup process initiates successfully and creates directories
• Progress stops at approximately 5% completion
• Backup fails with "BackupManager encountered an exception"
• Backup logs show NT_STATUS_SHARING_VIOLATION errors
• Directory creation succeeds but file transfers fail

 

Environment

• VMware vCenter Server Appliance (vCSA) 8.0 or later
• SMB backup target configured
• SMB server with connection limits configured

Cause

The issue occurs when the SMB server has insufficient concurrent connection limits configured. vCenter Server backup operations require multiple simultaneous SMB connections to perform various operations including:

• Writing backup data
• Verifying transfers
• Cleanup operations

When connection limits are too restrictive, the backup process cannot obtain the necessary connections to complete all required operations.

Resolution

For Windows SMB Servers:

1. Check SMB server connection limits:
   1. On the Windows server hosting the SMB share, open the share properties
   2. Navigate to Advanced Sharing
   3. Click Advanced Sharing Options
   4. Look for the connection limit setting
      
      
2. Modify connection limits:
   1. Set the connection limit to allow sufficient simultaneous connections
   2. If unsure of the optimal value, use the default unlimited setting

For Linux SMB Servers:

1. Check current Samba configuration:
   1. View the Samba configuration file:
      
            cat /etc/samba/smb.conf
      
      
   2. Look for the `max connections` parameter in the share definition
      
      
2. Modify connection limits:
   1. Edit the Samba configuration file:
      
            sudo vi /etc/samba/smb.conf
      
      
   2. Under the relevant share section, adjust or add:
      
            max connections = 0
      
      Note: 0 means unlimited connections
      
      
   3. Restart the Samba service:
      
            sudo systemctl restart smbd
      
      
3. Verify the solution:
   1. Attempt a new backup operation
   2. Monitor the backup progress to ensure completion
   3. Check backup logs for any remaining sharing violations

Additional Information

• Related symptoms may include failed cleanup operations and orphaned backup directories
• Consider monitoring SMB connection usage during backup operations to determine optimal connection limits
• For troubleshooting SMB connectivity issues, use the smbclient test commands:
  
  echo "Test backup content $(date)" > /tmp/test_backup.txt
smbclient //<server>/backups/ -U <username> -m SMB3 -c "put /tmp/test_backup.txt test_backup.txt"
  
  
• For Linux servers, monitor current connections using:
  
  smbstatus --processes