Distributed File System (DFS) Replication overview

Distributed File System (DFS) Replication is a Windows Server role service that lets you efficiently synchronize folders across multiple servers and sites. This article explains how DFS Replication works, its benefits, and how to get started.

DFS Replication is an efficient, active-active replication engine that you can use to keep folders synchronized between servers across limited bandwidth network connections. You can replicate all types of folders, including folders referred to by a DFS namespace path. The service replaces the File Replication Service (FRS) as the replication engine for DFS namespaces.

Tip

Consider using Azure File Sync to reduce your on-premises storage footprint. Azure File Sync can keep multiple Windows file servers in sync. Each server needs to only keep a cache on-premises while the full copy of the data is in the cloud. Azure File Sync also provides the benefit of cloud backups with integrated snapshots. For more information, see Planning for an Azure File Sync deployment.

DFS Replication uses a compression algorithm known as remote differential compression (RDC). RDC detects changes to the data in a file and enables DFS Replication to replicate only the changed file blocks instead of the entire file.

Active Directory Domain Services (AD DS) uses DFS Replication to replicate the sysvol folder in domains that use the Windows Server 2008 or later domain functional level. For more information about replicating the sysvol folder by using DFS Replication, see Migrate the sysvol folder replication to DFS Replication.

Understand replication groups

To use DFS Replication, you create replication groups and add replicated folders to the groups. Replicated folders are stored on servers in the group, which are referred to as members. DFS Replication establishes connections between the members of a group.

The following figure illustrates the relationship between a replication group, the members in the group, and the replicated folders.

A replicated folder stays synchronized on each member in a group. In the figure, there are two replicated folders: Projects and Proposals. As the data changes in each replicated folder, the changes are replicated across connections between the members of the replication group. The connections between all members form the replication topology.

Creating multiple replicated folders in a single replication group simplifies the process of deploying replicated folders. The topology, schedule, and bandwidth throttling for the replication group are applied to each replicated folder. Each replicated folder has unique settings, such as file and subfolder filters. The settings let you filter out different files and subfolders for each replicated folder.

The replicated folders stored on each member can be located on different volumes in the member, and the replicated folders don't need to be shared folders or part of a namespace.

Deploy and manage DFS Replication

DFS Replication is a part of the File and Storage Services role for Windows Server. You can install DFS Replication by using Windows Admin Center, Server Manager, or PowerShell. For detailed steps, see Install DFS Replication.

The management tools for DFS are the DFS Management snap-in, the DFS Replication PowerShell module, and the dfsradmin and dfsrdiag Windows Commands. These tools need to be installed separately and are available as part of the Remote Server Administration Tools (RSAT). The DFS Management snap-in simplifies sharing replicated folders and optionally publishing them in an existing namespace.

Interoperability with Azure virtual machines

DFS Replication on an Azure virtual machine is a verified scenario for Windows Server. However, there are some limitations and requirements for this implementation.

• Snapshots and saved states: to restore a server that's running DFS Replication, don't use snapshots or saved states to replicate anything other than the sysvol folder. If you attempt this type of restore, DFS Replication fails. This restoration requires special database recovery steps. Also, don't export, clone, or copy the virtual machines. For more information, see DFSR no longer replicates files after restoring a virtualized server's snapshot and Safely virtualizing DFSR.

• DFS Replication backups: to back up data in a replicated folder stored in a virtual machine, use backup software located on the guest virtual machine. Don't back up or restore a virtualized DFS Replication server from the host virtual machine.

• Domain controller access: DFS Replication requires access to physical or virtual domain controllers. The DFS Replication service can't communicate directly with Microsoft Entra ID.

• VPN connection: DFS Replication requires a VPN connection between your on-premises replication group members and any members hosted in Azure virtual machines. You also need to configure the on-premises router (such as Forefront Threat Management Gateway) to allow the RPC Endpoint Mapper (port 135) and a randomly assigned port between 49152 and 65535 to pass over the VPN connection. You can use the Set-DfsrMachineConfiguration cmdlet or the dfsrdiag Windows Command to specify a static port instead of the random port. For more information about how to specify a static port for DFS Replication, see Set-DfsrServiceConfiguration. For information about related ports to open for managing Windows Server, see Service overview and network port requirements for Windows.

To learn how to get started with Azure virtual machines, visit the Microsoft Azure website.

Next step

Learn how to install DFS Replication.