Details about the functionality and configuration of repositories supporting rotated media can be found in the Veeam Backup & Replication User Guide:
This registry setting is not required for rotated drives; it is provided here as an optional Backup file retention method. When this registry setting is enabled (set to 3 or 5), any repository, regardless of rotated media setting, will maintain retention normally until the job detects that previously-available files are missing.
Create this value on the Veeam Backup and Replication server:
Key Location: HKLM\SOFTWARE\Veeam\Veeam Backup and Replication\
Value Name: ForceDeleteBackupFiles
Value Type: DWORD (32 bit)
Value Data: (see below)
Value Data options:
Starting with Veeam Backup & Replication v9, all registry values are checked every 15 minutes, so a reboot will not be required, but the service must be given time to rescan the registry and find the new setting.
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