vCenter backups to SMB file server consistently fail after reaching approximately 95% completion

Products

• VMware vCenter Server

Issue/Introduction

• vCenter backup is attempted from VAMI.
• SMB (Server Message Block) Windows server is being used as the backup destination.
• Backups to the SMB file server consistently fail after reaching approximately 95% completion
• Some backup files are initially written to the file server, they are deleted following the failure. 
• if packets are captured at the vNICs of the vCenter appliance into a pcap/pcapng file, and the filter expression "tcp.analysis.flags && !tcp.analysis.window_update" is used at Wireshark, then the below TCP messages are displayed:
  
  
  • TCP Retransmissions
  • [TCP Out-Of-Order] messages
  • [TCP Previous segment not captured] messages 
  • TCP Dup ACK messages
  • NBSS Continuation Messages
  • Sharing a screenshot of these TCP flags as sample:
    
    
    
    
    
    
    
    
• vCenter logs at /var/log/vmware/applmgmt/backup.log may show the below log-lines:
  
  2025-11-21T15:12:35.696 [2025######-#########-248######] [VCDBBackup:PID#######] [VCDB::BackupVCDB:VCDB.py:######] ERROR: Failed to backup VCDB.
    raise BackupRestoreError('Failed to dispatch dump image of Postgres '

 

 

 

 

 

Environment

VMware vCenter Server

Cause

The above symptoms are strong indications of packet loss occurring between the vCenter and the SMB file server. All segments which are needed to correctly reassemble the complete NBSS message are not present, which is needed for SMB file sharing. Some segments are missing due to packet drops.

Resolution

 Follow up with your network and firewall teams, and identify location/reason for packet drops. 

Additional Information

The below KBs may be also relevant to vCenter Backup failure issues:

vCenter Server VAMI backup fails intermittently with Error: "BackupManager encountered an exception"

vCenter Server VAMI backup with NFS protocol fails with error "Failed to dispatch full database files"

Unable to change backup location in Vcenter VAMI and fails with an error - "General system error reported by backup server" when using SMB protocol

SMB backups failing with com.vmware.applmgmt.backup.plugin.timeout error