The Distributed file system (Dfs) is primarily a method of simplifying the view that users have of the available storage on a network—but it is also, when configured appropriately, a highly fault-tolerant storage mechanism. By configuring your Dfs root on a Windows 2000 domain controller, you can create a fault-tolerant, replicated, distributed file system that will give you great flexibility while presenting your
When you create a fault-tolerant Dfs root on a domain controller and replicate it and the links below it across multiple servers, you create a highly fault-tolerant file system that has the added benefit of distributing the load evenly across the replicated shares, giving you a substantial scalability improvement as well. See Chapter 16 for more on setting up your Dfs and ensuring that replication works correctly.
Windows 2000 Advanced Server supports two different kinds of clustering, either of which can greatly improve your fault tolerance:
The Network Load Balancing service (called Windows Load Balancing Service in Microsoft Windows NT 4) allows TCP/IP-based applications to be spread dynamically across up to 32 servers. If a particular server fails, the load and connections to that server are dynamically balanced to the remaining servers, providing a highly fault-tolerant environment without the need for specialized, shared hardware. Individual servers within the cluster can have different hardware and capabilities, and the overall job of load balancing and failover happens automatically, with each server in the cluster running its own Windows 2000 copy of Wlbs.exe, the Network Load Balancing service.
Server clusters, unlike network load balancing, depend on a shared resource between nodes of the cluster. This resource, which in the initial shipment of Windows 2000 Advanced Server must be a shared disk resource, is
Nodes in the cluster generally have identical hardware and identical capabilities, although it is technically possible to create a server cluster with dissimilar nodes. In the initial release of Windows 2000 Advanced Server, only two node clusters are supported for server clusters, although this restriction and the restriction on the type of shared resource are likely to change with later releases.
Server clusters provide a highly fault-tolerant and configurable environment for mission-critical services and applications. Applications don't need to be specially written to be able to take advantage of the fault tolerance of a server cluster, although if the application is written to be clustering aware, it can take advantage of additional controls and features in a failover and fallback scenario.
Building a highly available and fault-tolerant system requires you to