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BugZero found this defect 737 days ago.
Starting with Veeam Backup & Replication 12, the "Transform previous backup chains into rollbacks" option will become fully deprecated. The upgrade to Veeam Backup & Replication 12 cannot be completed if any Backup Jobs exist that are currently using the "Transform previous backup chains into rollbacks" option.
For Backup Jobs created in Veeam Backup & Replication versions prior to 11, there was an option to Transform previous backup chains into rollbacks. Starting in Veeam Backup & Replication version 11, this option was deprecated and the feature could no longer be selected in new jobs. However, jobs that were already using this feature would continue to do so after upgrading to Veeam Backup & Replication version 11. Starting with Veeam Backup & Replication version 12, this feature will be fully deprecated, and the presence of any jobs still using this feature will block the upgrade to Veeam Backup & Replication version 12. Simply disabling the "Transform previous backup chains into rollbacks" option may increase Repository space usage, as the job will begin using the Forward Incremental Backup Retention Policy which retains multiple sets of Synthetic Fulls on disk. Customers who enabled "Transform previous backup chains into rollbacks" to save space should consider using Forever Forward Incremental, which is enabled by unchecking both "Create synthetic full backups periodically" and "Transform previous backup chains into rollbacks."