FreeFileSync Open Source File Synchronization

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FreeFileSync User Manual:

Synchronization Settings

Synchronization settings dialog

Synchronization Variants

There are two basic synchronization variants depending on how many folders of a folder pair you are actively working on:

  • If both folders contain your work files and you want changes (creates, updates, and deletes) to flow in both directions, then select Two way. Database files are required to determine the directions and will be created automatically after the first sync.

  • If only one folder contains your work files and the other is for backup, then select the Mirror variant. The left folder will be the source and the right folder the target of the synchronization.

In order to handle special synchronization scenarios you can also set up Custom rules based on the categories determined after folder comparison.
The Update variant can be viewed as an example of such a customization: It is just like Mirror but adapted to avoid file deletions.

Detect Moved Files

FreeFileSync is able to detect moved files on one side and can quickly apply the same move on the target side during synchronization instead of a slow copy and delete. To make this work, FreeFileSync requires a file system that supports file IDs (as alternative to file paths) and database files ("sync.ffs_db") to compare the current file system state against the time of the last synchronization.

The Two way variant already creates database files, therefore, detection of moved files is always active.
The Mirror variant however, does not use the database files to find synchronization directions, so detection of moved files is not enabled by default. If you don't mind the creation of the database files, you can enable this feature by selecting the Detect moved files checkbox.

  • Detection of moved files is not yet possible when synchronizing a folder pair for the first time. Only beginning with the second sync the database files are available to determine moved files.
  • Detection is not supported on file systems that don't have (stable) file IDs. Most notably, certain file moves on FAT file systems cannot be detected. Also file accesses via SFTP do not support move detection. In these cases FreeFileSync will automatically fall back to "copy and delete".