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Supported only with the Microsoft Windows 2003 Enterprise Server and DataCenter Editions, Windows 2003 fault-tolerant options such as clustering and load balancing provide Exchange mailbox clients with high availability and performance when accessing Exchange 2003 messaging systems. This section provides information to assist administrators in understanding the functionality of Exchange 2003 in Windows 2003 clusters and NLB, environment features available with each, and best practices for determining which solution best fits your Exchange 2003 server needs. Clustering TerminologyBefore deciding which fault-tolerant option is best, here are a few terms used to describe the way clustered Exchange 2003 servers operate :
Fault-Tolerance OptionsMSCS and NLB services support Exchange 2003 messaging by establishing QOS when supporting server availability with back-end Exchange 2003 servers and high performance when supporting Outlook Web Access front-end systems. For these fault-tolerant clustering technologies to be truly effective, administrators must understand the characteristics of each in order to choose which technology and configuration best fits their Exchange 2003 Server design and messaging application service needs. Microsoft Cluster ServiceThe Microsoft Windows 2003 Cluster Service (MSCS) is a clustering technology that provides system-level fault tolerance by using failover. In Microsoft Exchange 2003 Server environments, cluster services are best used to provide access to mailbox information, Exchange 2003 resources such as public folders, and add-on applications such as virus wall systems and Internet mail bridgehead servers. When a problem is encountered with a Cluster Resource, the cluster service attempts to fix the problem before failing it completely. The cluster node running the failing resource attempts to restart the resource on the same node first. If the resource cannot be restarted, the cluster fails the resource, takes the cluster group offline, and moves it to another available node, where it can then be restarted. Several conditions can cause a cluster group to fail over. Failover can occur when an active node in the cluster loses power or network connectivity or suffers a hardware failure. When a Cluster Resource cannot remain available on an active node, the resource's group is moved to an available node, where it can then be restarted. NOTE In most cases, client communications can be affected by the failover process causing a short disruption in client/server communications. In some cases there may be no disruption. Cluster nodes can monitor the status of resources running on their local system, and they can also keep track of other nodes in the cluster through private network communication messages (heartbeats). The heartbeats are used to determine the status of a node and send updates of cluster configuration changes to the cluster quorum resource. The quorum resource contains the cluster configuration data necessary to restore a cluster to a working state. Each node in the cluster needs to have access to the quorum resource; otherwise , it will not be able to participate in the cluster. Windows Server 2003 provides three types of quorum resources, one for each cluster configuration model. To avoid unwanted failover, power management should be disabled on each of the cluster nodes, both in the motherboard BIOS and in the Power applet in the operating system's Control Panel. Power settings that enable a monitor to shut off are okay, but the administrator must make sure that the disks are configured to never go into standby mode. Network Load Balancing (NLB)The second clustering technology provided with the Windows Server 2003 Enterprise and DataCenter server platforms is Network Load Balancing (NLB). )NLB clusters provide high network performance and availability by balancing client requests across several server systems. When the client load increases , NLB clusters can easily be scaled out by adding more nodes to the cluster, to maintain or provide better response time to client requests. Network load balancing offers two great features : No proprietary hardware is needed to use load balancing, and an NLB cluster can be implemented and configured fairly easily and quickly. NLB clusters are most effectively used to provide front-end support for Web applications. In addition they are very effective solutions when used for application functionality, such as Outlook Web Access and Terminal servers. NLB clusters can grow to 32 nodes, and if larger cluster farms are necessary, the Microsoft Application Center server should be considered as an option for server platform support, along with technologies such as Domain Name System round- robin to meet this larger demand. NOTE When NLB clusters are configured, each server's configuration must be updated independently. The NLB administrator is responsible for making sure that configuration and information changes on each Exchange 2003 server are kept consistent across each node. For more information on installing load balancing with Exchange 2003 Server, refer to the section "Configuring Network Load Balancing with OWA," later in this chapter. Cluster Permissions with Exchange 2003 EnvironmentsUnlike previous versions of Exchange server in clustered environments, Exchange Server 2003 does not require the cluster server account to be a Full Exchange Administrator at the Exchange organization or administrative group levels. With Exchange 2003, the account logon permissions are used to establish rights for the Cluster Administrator to manage the Exchange 2003 cluster configurations. Using logon permission, the Cluster Administrator can create, delete, or modify Exchange virtual server configuration, depending on the level in which the permissions are applied and the mode (Mixed or Native) in which clustered Exchange 2003 organization is running. When working with Exchange 2003 Mixed and Native Mode cluster environments and multidomain models, some common best practices can be applied to help administrators understand how to set permissions to manage the Exchange cluster. With Windows 2003 multidomain models and child domain configurations, Cluster Administrator accounts require a minimum of Administrator Only permissions at the Exchange organizational level. This permission configuration is required to configure and apply Recipient Policies and configure the responsible server for providing the organization with the proper Recipient Update Services. In addition, when the Exchange 2003 organization is in Native Mode, if Exchange virtual servers are configured in routing groups and span multiple administrative groups, the Cluster Administrator must have Exchange Full Administrator permissions. This allows the account permissions to manage each administrative group and its Exchange virtual server members . Management Options with Exchange Server 2003When running Microsoft Exchange Server 2003 in clustered environments, administrators must implement clusters and load balancing technologies through Windows Server 2003. Microsoft Exchange Server 2003 does not provide any clustering technologies and management options for administering load balancing technologies.
Administrators can manage and configure clusters and load balancing options through the Windows 2003 Cluster Administrator snap-in. For more information regarding cluster management and configuration options, see the section "Managing Exchange 2003 Clusters," later in this chapter. |
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