vCenter VAMI SFTP backup fails due to destination server session duration limits - VMware vCenter Server

Products

• VMware vCenter Server

Issue/Introduction

• Manual or scheduled vCenter Server backups to an SFTP destination fail after a consistent duration (e.g., exactly 10 minutes or 60 minutes).
• The VAMI UI reports: "Internal error. See logs for details" or "Failed to create backup directory on backup server."
• In /var/log/vmware/applmgmt/backup.log, you see: ERROR: rc: 28, stderr: b'curl: (28) Timeout was reached\n' OR RC: 2, Err: curl: (2) Failure establishing ssh session: -43, Failed getting banner
• Manual connectivity tests (SFTP login, directory creation) from the vCenter shell work successfully for small files.

Environment

• VMware vCenter Server 7.0.x / 8.0.x
• SFTP Server: SolarWinds Serv-U or other security-hardened SFTP implementations.

Cause

This issue occurs when the destination SFTP server enforces a "Maximum Session Duration" or "Inactivity Timeout."

1. Session Limit: Servers like SolarWinds Serv-U often have a default session cap (e.g., 60 minutes).
2. No Resumable Upload: The vCenter VAMI backup uses a single continuous stream via curl. It does not support chunked transfers or resumable uploads.
3. Throughput vs. Payload: If the backup payload (e.g., including Stats, Events, and Tasks) is large and the network throughput is slow, the transfer time exceeds the server's allowed session window. The server then drops the connection, causing the backup to fail.

Resolution

To resolve this issue, perform one of the following:

1. Reduce Backup Payload Size:

   • In the VAMI backup configuration, deselect Stats, Events, and Tasks to back up only the core inventory and configuration. See: Manually Back Up vCenter Server by Using the vCenter Server Management Interface
   • Alternatively, reduce the vCenter Database Retention Policy to shrink historical data. See: Configure Database Settings

2. Adjust SFTP Server Settings:

   • Work with your SFTP server administrator to increase the Maximum Session Duration or Idle Timeout beyond the expected transfer time of the backup.

3. Change Backup Protocol:

   • Use SMB, NFS, or S3-compatible storage. These protocols generally do not enforce the same interactive session duration limits as hardened SFTP servers.

4. Optimize Network Throughput:

   • Investigate network bottlenecks or throttling between the vCenter Appliance and the SFTP server to ensure the transfer completes within the session window.

Additional Information

 If you continue to see banner errors after addressing timeouts, refer to KB 366953 to switch the file transfer mode from parallel to serial.