Choosing a Replication Topology

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

The replication topology describes the logical connections that FRS uses to replicate files among servers. To minimize the network bandwidth required for replication, identify where your bandwidth is highest and lowest on your network, and model your FRS replication topology after the physical topology of your network.

You use the Distributed File System snap-in to select a replication topology. After you add a second link target to a link, you are prompted to configure replication by using the Configure Replication Wizard, which allows you to perform the following tasks:

• Choose the initial master whose contents are replicated to the other targets. The initial master is only relevant during the creation of the replica set. After that, the server that acted as the initial master is treated no differently from any other server.

• Choose the location of the staging directory. By default, the staging directory is placed on a different volume than the content to be replicated.

• Choose the replication topology: ring, hub and spoke, full mesh, or custom. If you choose custom, you can add or delete connections to or from the replica set. For the other three standard topologies, you can only enable or disable connections between target servers.

The following describes the four topology types available in the Distributed File System snap-in. For an Excel spreadsheet to assist you in documenting your decision after you choose the topology, see "FRS Configuration Worksheet" (Sdcfsv_2.xls) on the Windows Server 2003 Deployment Kit companion CD (or see "FRS Configuration Worksheet" on the Web at https://www.microsoft.com/reskit).

Ring topology

Figure 2.10 illustrates a ring topology. In a ring topology, files replicate from one server to another in a circular configuration, with each server connected to the servers on either side of it in the ring. Choose a ring topology if your physical network topology resembles a ring topology. For example, if each server is located in a different site and has existing connectivity with neighboring servers, you can choose the ring topology so that each server connects only to neighboring servers. Because the ring topology is bidirectional, each connection is fault tolerant. If a single connection or server fails, data can still replicate to all members in the opposite direction.

Figure 2.10   Ring Topology

If you plan to create a ring topology with more than seven members, consider adding shortcut connections between some of the members to reduce the number of hops required for data to replicate to all members.

Hub and spoke topology

Figure 2.11 illustrates hub and spoke topology. In a hub and spoke topology, you designate one server as the hub. Other servers, called spokes, connect to the hub. This topology is typically used for WANs that consist of faster network connections between major computing hubs and slower links connecting branch offices. In this topology, files replicate from the hub server to the spoke servers and vice versa, but files do not replicate directly between two spoke servers. When you choose this topology, you must choose which server will act as the hub. If you want to set up multiple hubs, use a custom topology. Using multiple hubs is recommended, because using only one hub means that the hub is a single point of failure.

Figure 2.11   Hub and Spoke Topology

Full mesh topology

Figure 2.12 illustrates a full mesh topology. In a full mesh topology, every server connects to every other server. A file created on one server replicates directly to all other servers. Because each member connects to every other member, the propagation of change orders for replicating files can impose a heavy burden on the network. To reduce unnecessary traffic, use a different topology or delete connections you do not actually need. A full mesh topology is not recommended for replica sets with five or more members.

Figure 2.12   Full Mesh Topology

Custom topology

With a custom topology, you create the connections between the servers yourself. One example of a custom topology is a redundant hub and spoke topology. In this configuration, a hub site might contain two file servers that are connected by a high-speed link. Each of these two hub servers might connect with four branch file servers in a hub and spoke arrangement. An example of this topology is shown in "Example: An Organization Designs a Replication Strategy" later in this chapter. Figure 2.13 illustrates another type of hub and spoke topology known as a multitier redundant hub and spoke with an optional staging server used for introducing changes into the replica set.

Figure 2.13   Multitier Redundant Hub and Spoke Topology