Clustering the SQL Servers
To provide high availability for your SQL Server databases, it is recommended that you store them on server clusters using Cluster Service. Servers configured using Cluster Service share common data and work as a single system. Each server can operate independently of other servers in the cluster. So if one server fails, another server takes over its functions.
Each node has its own memory, system disk, operating system, and subset of the resources in the cluster. If one node fails, another one takes ownership of the resources of the failed node. The cluster service then registers the network address for the resource on the new node so that client traffic is routed to the new server. When the failed server is brought back online, the cluster service can be configured to redistribute resources and client requests.
There are several server clustering techniques, including shared disks and mirrored disks, to consider using, depending on your needs and budget. Also, you can configure your servers as active/active, in which each server runs applications while also serving as a backup for the other server, or active/passive, in which one server runs applications while the other one serves as a backup. Making these decisions requires that you consider the role of server clusters in your site. The following table lists three techniques you can use to make disk data available to more than one server.
| Technique | Description |
|---|---|
| Shared disk | Although no longer requiring expensive cabling and switches, the shared-disk technique (in which multiple servers share the same disk) still requires specially modified applications using software called a Distributed Lock Manager (DLM). |
| Mirrored disk | More flexible than the shared-disk technique, the mirrored-disk technique is based on each server having its own disks, and using software that "mirrors" every write from one server to a copy of the data on another server.
This technique is very useful for keeping data at a disaster-recovery site synchronized with a primary server. |
| Shared nothing | In a shared-nothing architecture configuration, each server owns its own disk resources. If a server fails, a shared-nothing cluster has software that can transfer ownership of a disk from one server to another.
This technique provides the same high level of availability as shared-disk clusters, with potentially higher scalability, because it does not have the inherent bottleneck of a DLM. |
Before creating server clusters, you need to plan for them carefully. The servers in the cluster must be configured with compatible disk drives, network adapters, and disk controllers. For more information about these requirements, consult your hardware vendor. For more information about planning for server clusters, see the Microsoft Windows 2000 Server Deployment Planning Guide. After you develop a server cluster plan, use the Windows Cluster Service Configuration Wizard to create and configure your server cluster. For prescriptive information on installing Cluster Service, see the Step-by-Step Guide to Installing Cluster Service.
Cluster the SQL database using Windows clustering. For a detailed example, see “Commerce Server 2000 High Availability Reference Architecture: Compaq-Microsoft High Availability Reference Architecture Validation,” available from https://go.microsoft.com/fwlink/?LinkId=6687.
For information about installing Direct Mailer and Predictor on a cluster, see Installing Commerce Server 2002 Resources as Clustered Resources.
See Also
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