Windows 2000 Advanced Server provides a powerful set of features that help ensure that mission-critical applications and resources remain continuously available. This section introduces symmetric multiprocessing (SMP), clustering, network load balancing, and COM+ load balancing (available in Microsoft Application Center 2000) and shows how these technologies work together to enable high availability of critical applications, databases, and Web services.
Symmetric Multiprocessing (SMP)
SMP lets software use multiple processors on a single server in order to improve performance, a concept known as hardware scaling, or scaling up. Any idle processor can be assigned any task, and up to 8 CPUs can be added to improve performance and handle increased loads. Improvements in the implementation of SMP code allow for improved scaling linearity, making Advanced Server a powerful platform for critical applications, databases, and Web services.
Clustering
Clustering provides users with constant access to important server-based resources. Windows 2000 Advanced Server provides the system services for two-node server clustering. With clustering, you create two cluster nodes that appear to users as one server. If one of the nodes in the cluster fails, the other node begins to provide service in a process known as failover. Combined with advanced SMP and large memory support in Windows 2000 Advanced Server, Windows clustering technologies enable organizations to ensure the availability of critical applications while being able to scale those applications both up and out to meet increased demand.
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igure 2: Windows Cluster service.
By providing redundant servers, clustering virtually eliminates most of the reliability issues with an individual server. Clustering addresses both planned sources of downtime—such as hardware and software upgrades—and unplanned, failure-driven outages. With Windows 2000 clustering, administrators can upgrade computers more efficiently by taking advantage of rolling upgrades. This lets you upgrade a machine in a cluster that is not handling user loads; when the upgrade is complete, users are switched to the upgraded machine. Rolling upgrades eliminate the need to reduce the availability of a server when software is upgraded.
Network Load Balancing
Another way to improve the availability of Windows 2000 systems is through the use of network load balancing. To handle large amounts of traffic more efficiently, network load balancing routes incoming requests to one of several different machines.
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igure 3: Network Load Balancing.
Network Load Balancing (NLB) is implemented through the use of routing software associated with a single IP address. When a request comes into that address, it is transparently routed to one of the servers participating in load balancing. NLB is especially important for building Web-based systems, where the demands of scalability and 24 x 7 availability require the use of multiple systems.
Load balancing, in conjunction with the use of “server farms,” is part of a scaling approach referred to as scaling out. The greater the number of machines involved in the load balancing scenario, the higher the throughput of the overall server farm. Load balancing also provides for improved availability, as each of the servers in the group acts as "live backup" for all the other machines participating in the load balancing. Windows 2000 NLBS is designed to detect and recover from the loss of an individual server in the group, which reduces maintenance costs while increasing availability.
To learn more about the Clustering technologies in Windows 2000 Advanced Server, see “Introducing Windows 2000 Advanced Server” at http://www.microsoft.com/windows2000/guide/server/solutions/overview/advanced.asp.
Component Load Balancing
The newly released Microsoft Application Center 2000 will go beyond NLBS to include Component Load Balancing. With Component Load Balancing, Windows 2000 can balance loads among different instances of the same COM+ component running on one or more machines that are running Application Center 2000. To add flexibility to distributed Web applications, you can use Component Load Balancing in conjunction with Network Load Balancing Services. A system with Network Load Balancing Services, COM+ Load Balancing, and clustering is shown in Figure 4 below.
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igure 4 – A highly redundant system solution can combine Network Load Balancing, Component Load Balancing, and clustering.
For additional technical information Component Load Balancing, see http://www.microsoft.com/applicationcenter/techinfo/CLB.doc.
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