NSX Manager UI reports backup success but 0-byte files are written to the backup server

Products

• VMware NSX
• VMware Cloud Foundation

Issue/Introduction

The NSX UI reports the backup as "Successful," but the actual backup files (db.tar and fs.tar) on the SFTP server are 0 bytes.

In some scenarios, the files may not be exactly 0 bytes, but they will be abnormally small (e.g., just a few KB or MB) compared to your typical backup size.

Alternatively, the backup may fail entirely, displaying the following error in the NSX UI: "Either sftp server disk full or bad directory path or check if the directory path length is beyond 260 character limit on windows server.

When this failure occurs, a corresponding error is recorded in the Proton logs (/var/log/proton/nsxapi.log).

2026-09-27T20:49:44.243Z ERROR NSX 7654 [nsx@4413 comp="nsx-manager" errorCode="MP29111" level="ERROR" logger="ClusterNodeBackupJob" s2comp="backup-restore" subcomp="manager" threadName="scheduling-worker-1"] Cluster backup failed with ; BackupAsyncStatus [BackupStatus [status=URI_NOT_FOUND, statusDetail=Specified uri '/VCF-INT-Backup/nsx-bkp/9.1.1.0.25691516-IPv4-########-####-####-####-############-10.2.79.19/backup-2026-09-27T20_49_10UTC/db.tar' not found., remoteUri=sftp://<SFTP FQDN>:22/VCF-INT-Backup/nsx-bkp/9.1.1.0.25691516-IPv4-########-####-####-####-############-10.2.79.19/backup-2026-09-27T20_49_10UTC/db.tar, errorCode=null, startTime=1790542158509, endTime=1790542184210]; responseBody=null].

Environment

VMware NSX
VMware Cloud Foundation (VCF) 

Cause

The issue occurred because the SFTP server ran short of disk space. NSX Manager copies each backup file to the SFTP server with the sftp client (a PUT), which transfers the file in chunks. If the server has less free space than the backup file needs, the transfer stops when the space runs out. The server then holds only part of the file, or an empty file. There is a missing validation from NSX side to cross check the size of the backup file on the SFTP server post completion of the operation due to which backup is wrongly marked as success. 

Resolution

This is a known defect that is scheduled to be fixed in NSX version 9.2

Workaround:

Verify the available storage space on the destination backup server and ensure there is adequate capacity to accommodate the backup files.