Veeam Legacy Backup Chain Format Blocks the Upgrade

Signal

The upgrade run halts at the gate with LegacyChainFormat - N legacy-format backup(s) of M, and nothing is installed.

Cause

Veeam 13 does not support per-job (legacy) backup chains: one shared metadata file for every machine in the job. It needs per-machine chains. The upgrade gate checks each backup's IsMetaExist flag; True means a legacy chain.

Removing the backup on its own doesn't fix it. If the repository is still set to per-job files, the job's next run writes a new legacy chain. The repository setting has to change first. This was converted on 12 BDRs during the v13 upgrade.

Before you start

• Check free space. Step 4 writes a fresh full backup. The repository needs room for a complete full on top of what it already holds.
• The old restore points stay on disk after step 3, and can be re-imported. Nothing is deleted until you choose to in step 7.

Procedure

1. Switch the repository to per-machine files. In the Veeam console: Backup Infrastructure → Backup Repositories → <repository> → Edit → Repository → Advanced, and tick Use per-machine backup files. Or in PowerShell (pwsh on 13.x):

   Set-VBRBackupRepository -Repository (Get-VBRBackupRepository -Name '<repository>') -UsePerVMFile
   

2. Stop the job if it's running.
3. Remove the legacy backup from the configuration — not from disk. In the console: Backups → Disk, right-click the backup → Remove from configuration. The files stay where they are.
4. Start the job. It writes a new per-machine chain, beginning with a full.
5. Confirm the new chain is per-machine:

   & pwsh -NoProfile -Command { Import-Module Veeam.Backup.PowerShell -DisableNameChecking -WarningAction SilentlyContinue; Get-VBRBackup | Select-Object Name, IsMetaExist }
   

   Every backup should read IsMetaExist : False.
6. Re-run Veeam v13 Upgrade. The gate passes.
7. Reclaim the space once the new chain has completed and been verified. The old chain's folder is now orphaned — Veeam no longer tracks it — and can be deleted. On one BDR it held 3.47 TB.

Rollback

Until step 7, the old chain is intact on disk. To restore from it, use Backups → Import Backup in the console and point it at the old folder's metadata file.

If it comes back

If the gate reports a legacy chain again after conversion, check the repository setting again: the job may be writing to a second repository that still uses per-job files, or the setting may have been reverted. Then repeat from step 2.

Related

• BDR Storage Alerts & Capacity Issues
• Veeam Setup Failure Reference (13.1.1.18)
• Veeam BDR Script Toolkit
• NinjaOne Veeam Alerts & Custom Fields — Where to Start