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New Microsoft Cluster.

Former Member
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Years ago i did many SAP in the Microsoft Cluster Environment. I have to say that I like it, some problems can occour but the system was reliable.

At this moment we're planning new environments for the HCM servers. The Microsoft Cluster has been choosen as the main HA system. Well, I have read some documentation and many thinks are changed. The first in the new idea of the SPOFs ( single point of failures ) are the only that will be clusterized and the application servers will be installed in the local machines.

I need some clarification. We're not planning to have Application servers. Only one instance will be enough. Can I clusterize the dialog instance to avoid the local installation as I did in the past ? There is something i'm missunderstanding.

Best regards.

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Answers (1)

Answers (1)

Former Member
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The new (Netweaver 7.0) way of handling the cluster is what you describe and you can not install the Central Instance "the old way".

The new solution uses MSCS to cluster the Enqeue and Message Server (called ASCS for ABAP and SCS for Java).

Let's assume an ABAP-installation.

If you have node A and B and node A is running the ASCS.

Then node B is running an enqueue replication service.

It's purpose is to mirror the locks in the system so the locks are not lost during fail-over.

On node A you install the local Central Instance

(well, since what's really makes the central instance is the ASCS it is actually an Dialog Instance).

on node B you install an local Dialog Instance.

If node A crashes, the ASCS makes a fail-over to node B

and the local Dialog Instance takes the load.

When node A comes back all users still accessing node B.

The Enqueue Replicator on node A starts automatically.

But here is the drawback.

You have to start the Central Instance on node A manually with SAPMMC.

Otherwise, if node B crashes the ASCS fail-over to node A,

but there is no Instance running which can take the user load.

There are ways to make the CI and/or DI to start automatically,

but most SAP administrators want to have the control themselves.

If you shutdown the cluster completely (e g due to maintenance).

- Stopp both Instances (CI + DI) with SAPMMC.

- Stopp Enqueue Replication Services with SAPMMC.

- Stopp ASCS (MSCS)

When starting the cluster again (e g after maintenance).

- Start ASCS (MSCS)

- Start Enqueue Replication Services with SAPMMC (after reboot, these starts automatically).

- Start both instances (CI + DI) with SAPMMC.