NSX Backups fail with "sftp server disk full" or "URI NOT FOUND" due to non-standard SFTP server responses

Products

• VMware NSX

Issue/Introduction

NSX Manager cluster backup fails when targeting a Linux-based SFTP server. While connectivity and permissions appear correct, the backup process terminates because the SFTP server returns non-standard error codes that the NSX Manager cannot interpret.

• NSX UI Error: 

  Either sftp server disk full or bad directory path or check if the directory path length is beyond 260 character limit on windows server

• NSX Log Error (syslog/proton-audit.log): 

  BackupAsyncStatus [BackupStatus [status=URI_NOT_FOUND, statusDetail=Specified uri '/exampledir' not found... errorCode=null]

Environment

VMware Cloud Foundation 9.x

VMware NSX 4.x

Cause

The SFTP server implementation returns an incorrect error message—remote mkdir "/path": No such file or directory—when the NSX Manager attempts to create or validate a directory that already exists. NSX expects standard POSIX/OpenSSH responses (e.g., File exists or Failure). The non-standard "No such file" response causes NSX to incorrectly conclude the target URI is invalid or unreachable. 

Resolution

RESOLUTION

1. Manual Validation: Log into the NSX Manager CLI and establish a manual SFTP connection to the backup server:
   bash

   sftp <SFTP_USER>@<SFTP_SERVER_IP>

2. Test Directory Creation: Navigate to the target directory and attempt to create a folder that already exists:

   mkdir <EXISTING_DIRECTORY_NAME>

3. Analyze the Response:
   • Standard Behavior: Server returns 

     mkdir: cannot create directory 'dir': File exists or remote mkdir "/path": Failure.

   • Issue Behavior: Server returns remote

     mkdir "/path": No such file or directory

4. Correction: 
   
   If the Issue Behavior is observed, the fault lies with the SFTP server configuration.

• • Coordinate with the Linux/Security administrator to review sshd_config for non-standard ChrootDirectory or ForceCommand settings that may be altering return codes. 
  • If the third-party SFTP software cannot be configured to provide standard responses, migrate to a supported SFTP server implementation.

Additional Information

For a list of tested and supported SFTP servers, refer to the Broadcom TechDocs: Configure Backups