Expert settings

FreeFileSync has a number of special purpose settings that can only be accessed directly via the global configuration file "GlobalSettings.xml". To locate this file enter "%appdata%\FreeFileSync" in the Windows Explorer address bar or go to the FreeFileSync installation folder if you are using the portable installation.

<?xml version="1.0" encoding="UTF-8"?>
<FreeFileSync XmlType="GLOBAL">
    <Shared>
        <FileTimeTolerance Seconds="2"/>
        <RunWithBackgroundPriority Enabled="false"/>
        <LockDirectoriesDuringSync Enabled="true"/>
        <VerifyCopiedFiles Enabled="false"/>
        <LastSyncsLogSizeMax Bytes="100000"/>

FileTimeTolerance:
By default file modification times are allowed to have a 2 second difference while still being considered equal. This is required by FAT/FAT32 file systems which store file times with a 2 second precision only.
This setting can also be used to simulate a "compare by file size", ignoring last modification times: If tolerance is set to some high value, e.g. 2.000.000.000, then changed files will be detected as a conflict (same date, different file size) and the synchronization direction for conflicts can be set accordingly.

RunWithBackgroundPriority:
While synchronization is running, other applications which are accessing the same data locations may experience a noticeable slowdown. Enable this setting to lower FreeFileSync's resource consumption at the cost of a significantly slower synchronization speed.

LockDirectoriesDuringSync:
In order to avoid race conditions of multiple FreeFileSync instances writing to the same folder at the same time, accesses are serialized by lock files ("sync.ffs_lock"). This allows to operate FreeFileSync with an arbitrary number of users in a network out of the box.

VerifyCopiedFiles:
If active FreeFileSync will binary-compare source and target files after copying and report verification errors. Note that this may double file copy times and is no guarantee that data has not already been corrupted prior to copying and corruption is not hidden by deceptively reading valid data from various buffers in the application and hardware stack.
Does the CopyFile function verify that the data reached its final destination successfully?

LastSyncsLogSizeMax:
The progress logs of the most recent synchronizations (for both GUI and batch jobs) are collected automatically in the file "LastSyncs.log". The maximum size of this log file can be set here.