Using FreeFileSync to Investigate Large Backups



This article explains how to use the FreeFileSync application. 


  • FreeFileSync


FreeFileSync is an open source tool that you can use to identify growth and change between backup snapshots. The application presents differences in a text format that is easy to understand.


1. Download FreeFileSync from the developer's website. Datto does not recommend downloading the application from any third-party websites.

Figure 1: FreeFileSync download link 

2. Install the application on a workstation on the same LAN as your Datto appliance by using the appropriate installer. Be sure to read all prompts during the installation process, and only allow FreeFileSync to install.

3. Log in to the GUI of your Datto appliance, and mount two file restores. One restore should be from the date when the large backup happened. The other restore should be from the time and date just before the size of the backup increased.

4. Launch FreeFileSync. The central application window is divided into two panes, allowing you to browse to separate locations.

  • In the left pane, click Browse, and browse to the network path of the file restore from the older point.
  • In the right pane, click Browse, and browse to the network path of the file restore with the most recent point.

Figure 2: FreeFileSync UI

5. Click on the blue Compare icon at the top of the screen to begin the comparison process. Depending on the number of volumes and the size of the server, the comparison can take some time to run.

6. After the comparison completes, FreeFileSync will list all files for both restore points mounted. You can sort through the files to see which are new, removed, replaced, or moved. Also, the Overview pane can provide a report of where the largest changes were detected.

Figure 3: FreeFileSync comparison report

Additional Resources

Free File Sync tutorial videos (external link)
Free File Sync user manual (external link)

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