How Do I Use WinMerge to Investigate Large Backups?



This guide explains using WinMerge to investigate changes within backups.


  • Datto SIRIS
  • Datto ALTO
  • Datto NAS
  • WinMerge (Installed or Portable)
  • Microsoft Visual C++ 2008 Runtime Components
  • Microsoft Windows XP/2003/Vista/2008/7/8/2012


WinMerge is a free, third-party 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.

NOTE: WinMerge does not appear to produce consistent results with Windows Server 2016 backups. Should you encounter technical difficulties with the application, please contact WinMerge via their Support forum (external link).


1. Download WinMerge from the developer websiteDatto does not recommend downloading applications from any third-party websites.

Figure 1: Download and install WinMerge

2. Install the application on a server or workstation on the same LAN as the Datto appliance by using the appropriate installer. Be sure to read all prompts during the installation process, and only allow WinMerge to install. If installing the portable version, ensure that Microsoft Visual C++ 2008 Runtime Components are installed prior to using.

3. Log into the Datto appliance's web UI and mount two file restores. One restore should be from the date when the large backup happened, the other should be from the time and date just before the size of the backup increased.

4. Launch WinMerge and go to Edit > Options... > Compare > Folder and change the compare method dropdown to Modified Date and Size.

Figure 2: Change the Compare method

5. In the Restore tab of the Web UI, obtain the the network paths for both file restores.

6. In WinMerge, go to File > Open... In the Left field, enter the network path of the older file restore. In the Right field, enter the network path of the more recent file restore. Leave the Filter field as *.* to compare all file extensions. Check the Include Subfolders box.

Figure 3: Enter the file paths

7. Once the above fields are populated, choose OK. The Comparison result, Left Date, and Right Date columns will show modifications to files.

img4.pngFigure 4: View comparisons

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