Specifications

14 Optimizing IBM Netfinity Servers for SAP R/3 and Windows NT
1.8.4 Clustering
For an additional level of high availability, clustering solutions for your Netfinity
Servers are obtainable. IBM offers a diversity of high-availability clustering
choices:
• Microsoft Cluster Server (MSCS) for a shared-disk configuration
• Vinca High Availability offerings for a shared-disk configuration
• Vinca StandbyServer for a mirrored-disk configuration
A clustering solution will prevent the R/3 System from being unavailable for the
customer if a hardware or software failure occurs. For the SAP R/3 and Windows
NT environment it is only important to take the Microsoft Cluster Server into
consideration. IBM does not offer or support other solutions than MSCS in the
SAP R/3 environment. Microsoft Cluster Server is currently available as a part of
Windows NT Server Enterprise Edition.
Microsoft Cluster Solution is divided into three phases. Only the first phase is
finished and released.
The first phase of the Microsoft Clustering Solution is a failover solution with two
nodes in a cluster which have access to a shared disk subsystem. But only one
server gets access to a disk resource at time. This technology is known as
shared
disk but shared nothing
.
Both nodes are available to run applications at the same time. Figure 5 shows an
example of a clustered SAP R/3 environment, where one node becomes the
database server and one an application server with the central instance. Central
instance includes the message server and the enqueue server together. These
three components must be running to keep the R/3 system available to the
customer.
Figure 5. Example of a Clustered SAP R/3 Environment
If a hardware or software error occurs, the surviving server will take over all
resources and restart the applications. This process is known as
failover . If the