Reducing Windows ISO Size

Reducing Windows ISO Size #

If you attempt to upload a Windows ISO containing an install.wim file larger than 4 gigabytes, the unpack operation will fail due to the size of the install.wim file. A quick way around the issue is to extract the image from the file and creating a new install.wim file smaller in size.

This documentation is for Synergy 4.x and older. Synergy 5.0+ properly handles install.wim sizes larger than 4 gigabytes.

Install wimlib #

Download the latest stable version of wimlib from, follow standard tar.gz file install steps. Installation from your distro’s package manager is not recommended as the package repo’s version could be significantly out of date.

Some additional libraries may need to be installed if errors occur during install.

Finding the image index #

Once wimlib is installed, mount or unpack the Windows ISO, find the install.wim file, and run:

wiminfo /directory path/install.wim

The output will list all versions in the file, locate your desired version and its index.

Extracting and recompressing the image #

Once you know the index of your version you can extract the image into a new install.wim file.

Create a new folder for the version to avoid confusion with your current install.wim file.

To extract and create the file run:

wimexport currentfilepath/install.wim <index> newfolderpath/install.wim --compress=lzx

Once the extraction is done the new file will be created and you can verify the file by running the wiminfo command from above.

If the command above doesn’t get install.wim under 4 gigabytes, wimlib’s page on compression has several other options you can try.