Overview of Windows Clustering Technologies

To provide administrators with advanced capabilities for managing enterprise and commercial network servers, Microsoft has integrated clustering technologies into the Windows 2000 operating system. This lesson will introduce you to Cluster Service and NLB. Although both technologies provide solutions for increased server availability and efficiency, they are complementary technologies. This lesson explains when you might implement one service over the other and when you might consider implementing both.

Before you implement a clustering technology, you must decide on an appropriate operating system. Not all of the Windows 2000 operating systems support the clustering technologies. This lesson describes some of the key differences among the Windows 2000 family of servers in regard to clustering support.


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Cluster Service and NLB
In Windows NT Server Enterprise Edition, Microsoft introduced a technology that allowed organizations to increase the availability of servers that hosted mission-critical applications by grouping servers. If one server failed, another one would assume its responsibilities. This technology was called Microsoft Clustering Server, or MSCS. MSCS was designed to group multiple physical servers that had access to a shared drive array, so that they could act as a single network server. Clients would access the applications using a single computer name as if the cluster were a normal server. The MSCS service would monitor the health of each server, or node, within the cluster. If one were to fail, MSCS would move the responsibility for hosting an application to another node. Since network clients would be using a server name managed by MSCS, they would not have to be reconfigured each time an application was moved from a one node to another.

In Windows 2000, MSCS has been updated and renamed Microsoft Cluster Service. Cluster Service provides added benefits and is easier to install.

Microsoft Windows NT Enterprise Edition also came with Windows Load Balancing (WLB) technology, which allowed administrators to group many servers so that each could respond to client requests. For example, a large commercial Web site that handles millions of client requests is actually a group of servers responding to these requests. WLB was designed to provide this functionality across many servers. In Windows 2000, WLB has been updated and renamed Network Load Balancing.

When to Implement a Cluster
Clustering can be beneficial in a number of scenarios. You should consider a cluster when your network services require a high degree of availability, such as when you have an e-commerce site that processes live transactions based on customer orders. Here are some of the possible reasons to implement a cluster:

To reduce downtime due to routine maintenance or unplanned failures
To perform upgrades to nodes, resources, and applications without interrupting client access
To perform rolling upgrades (operating system upgrades that do not interrupt client access)
To increase server availability for mission-critical applications and network services
To take advantage of cluster-aware applications such as Microsoft Exchange Server or Microsoft SQL Server
The following table lists some specific scenarios and the clustering technology you can use in each.

Cluster Scenarios
Scenario Cluster Service NLB
Web server farm
No
Yes

File/print server
Yes
No

Database/messaging application
Yes
No

E-commerce site
Yes
Yes


You should consider using NLB for a Web server farm because it allows for rapid expansion. File and print servers and database or messaging applications should use Cluster Service because these require a high level of availability. Many e-commerce sites can benefit from both clustering technologies because they require a high level of availability, performance, and expandability.

Choosing an Operating System
Not all Windows 2000 operating systems support clustering. In order to support clustering, the operating system must be able to

Create and delete network names and addresses dynamically
Modify the file system to close open files during a drive dismount
Modify the I/O subsystem to share disks and volume sets among multiple servers, or nodes, in the cluster
Currently, only Windows 2000 Advanced Server and Windows 2000 Datacenter Server provide all three of these capabilities. Windows 2000 Server, which supports up to four microprocessors and 4 GB of physical memory, is intended as a general-purpose server operating system, so it does not support advanced features such as Cluster Service or NLB.

Windows 2000 Advanced Server
Windows 2000 Advanced Server provides greater scalability and availability than Windows 2000 Server. It supports up to 8 GB of physical memory and can scale up to eight processors. Support for Cluster Service and NLB is integrated into the operating system and allows you to connect two servers to form a cluster.

Windows 2000 Datacenter Server
Windows 2000 Datacenter Server is the most powerful server operating system that Microsoft offers. It supports up to 32 processors and 64 GB of physical memory, and includes Cluster Service and NLB as standard features. Windows 2000 Datacenter Server supports clusters of up to four servers. It is thus designed to support large-scale enterprise environments such as

E-commerce and online transaction processing (OLTP)
Leading Internet service providers (ISPs) and Web hosting
Large data warehouses and data centers
Science and engineering simulations
Lesson Summary
Originally introduced as Microsoft Clustering Server and Windows Load Balancing in the Windows NT operating system, the two clustering technologies supported by the Windows 2000 family of servers are known in their updated form as Microsoft Cluster Service and Network Load Balancing.

Cluster Service increases the availability of servers hosting mission-critical applications. NLB is appropriate when multiple servers must manage a high number of network requests, such as when a large commercial Web site is hosted by many physical Web servers. Ultimately, your organization's requirements for clustering or load balancing will determine which Windows 2000 operating system you deploy. If you do not need to implement either clustering technology, Windows 2000 Server might suffice. If you need only two-node cluster support or basic NLB, you should deploy Windows 2000 Advanced Server. Organizations requiring two-node to four-node clustering, NLB, and maximum scalability should deploy Windows 2000 Datacenter Server.