How does CBB local file backups handle moved data?
No need to do repository sync. In either format, files would be backed up all over again, and the original location backups would be deleted from backup storage based on your retention setting for deleted files.
Synthetic fulls do not work for local storage, so move the files, run the backups, make sure you have a setting for purging of deleted files set and you will be fine.
The problem with the new format is that you have to do periodic true full backups (where all files get backed up regardless of whether they have been modified. And you have to keep at least two generations. That is not the case for the legacy format, so we use legacy for local and cloud file backups. We use the new format for Cloud image and VHDx backups as BackBlaze supports synthetic fulls, but we still need to keep two generations, which takes up twice the storage.
But it is worth it to get the backups completed in 75% less time thanks to the synthetic ful capability.
Sorry if this is confusing,