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How to create "Active-Active" SAP Central Instance Cluster on Windows 2000/2003

In this article, i’ll show you how to install an “active-active” cluster node used for SAP Central Instance (CI) and Dialog Instance (DI) on Windows 2000/2003 Server using WAS 6.40 or below.
In common SAP – MSCS cluster you can only use one node as SAP CI, while the other node is passive, commonly used for DB instance. In fact we can make other node also active as DI while CI residing in other node.
How-to-setup-active-active-SAP-cluster
Common Cluster Configuration

Sometimes you move out DB server to separate machine, making your CI other cluster node is idle in normal operation. It will be functioning when switch over happen. As depicted in picture below.

Separate DB server
However We can make the idle node to be functioned as SAP Dialog Instance as depicted below, and it’s functioned as load balancing SAP application server.

 

Other CI node is functioning as SAP DI
We will use the usage of Windows linkd (provided in Windows Resource Kit).

The key is the folder placement in local disk and shared storage. In common cluster configuration, the executable is located in shared storage. In our case we put SAP Central Instance executable in both server’s local folder and create junction to shared storage as depicted below.

How to setup “active – active” SAP Cluster node
Before you do the CI installation (make sure you have created cluster resource group contains shared folder for SAP Executable).
1. prepare empty folder C:\usr\sap\\DVEBMGS00 and C:\usr\sap\\SYS in both nodes.
2. After that You create those folders in shared storage X:\usr\sap\\DVEBMGS00 and X:\usr\sap\\SYS in both nodes. .
3. In node 1, run command linkd C:\usr\sap\\DVEBMGS00 X:\usr\sap\\DVEBMGS00 it will create link for those folders.
4. run command linkd C:\usr\sap\\SYS X:\usr\sap\\SYS
5. Move shared storage (X:) to node 2.
6. Run command 3 & 4 for node 2.
7. Now you are ready to install SAP CI in node 1 & node 2 (use X: as installation folder)
8. After you finish installing in both node, you can install passive node with Dialog Instance
9. Installation is finished, now you can start both instances.
At the end, in node A you have CI and in node B you have DI, you can put them in SAP Logon Load Balancing, it means both servers are fully functioning as active – active to share load without disturbing your SAP High Availability solution.

If you want to know more about SAP High Availability solution in Windows environment you can read this book SAP on Windows.

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