File Replication Service is a Microsoft Windows Server service for distributing folders stored in the SYSVOL shared folder on domain controllers and Distributed File System (DFS) shared folders.
When the File Replication Service (FRS) detects a change to a file, such as the creation of a new file or the modification to an existing file, it replicates it to other servers in the group.
One of the main uses of FRS is for the SYSVOL directory share. The SYSVOL directory share is particularly important in a Microsoft network as it is used to distribute files supporting Group Policy and scripts to client computers on the network. Since Group Policies and scripts are run each time a user logs on to the system, it is important to have reliability. Having multiple copies of the SYSVOL directory increases the resilience and spreads the workload for this essential service.