Difference between ASCS and CI

[Former Member]

Hi Experts,

I am a bit confused with the difference between the terminologies ASCS and CI. With the introduction of ASCS the Message and Enqueue services are separated from CI then why does CI terminology still exists in the installation guide or for that reason why do we still have to install CI in HA set up?

What services will be there in CI with the existence of ASCS? Will the CI still hold Message server and Enqueue server and will be a replica of ASCS?

The simplest HA setup what I understand is this-

Node A- ASCS + CI + DB (With DB and ASCS as SPOFs and clustered)

Node B - DI

So with this when Node A fails ASCS and DB gets moved to Node B and DI on Node B takes the place of CI. But my confusion here is if DI is taking the place of CI then CI and and DI becomes same in the whole architecture. Is it so?

Regards

Sourabh Majumdar

[Former Member · Accepted solution]

Hello Sourabh,

I was wondering about the central instances right to exist as well.

Taking into consideration that enqueue service and message service now exist in the ASCS instance, there really isn't much difference between the so-called central instance and a simple dialogue instance.

There is one major difference though: In an HA environment only one dialogue instance may be made highly available, so that it will fail over in case of a failure. And somehow SAP decided to call this instance the central instance. For historical reasons I presume.

regards

[Former Member · Accepted solution]

>

> There is one major difference though: In an HA environment only one dialogue instance may be made highly available, so that it will fail over in case of a failure. And somehow SAP decided to call this instance the central instance. For historical reasons I presume.

>

> regards

no dialog instance and CI is highly available in HA. only ASCS and DB instances are highly available in HA. So, in case of failure on any one of the node other node will take over. CI and Dialog instance role is same.

Thanks

Sunny

[Former Member · Accepted solution]

Sunny,

in our environment central instance was made highly available, by means of Oracle RAC and sapctl.

It seems nowadays you may even make more than one dialogue instance HA.

For more information:

http://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/80fab80e-228c-2d10-e196-f268c4c16...

There is also, as a partly answer to Sourabh's question, on page 11:

In case of the ABAP application stack, it is still required to configure a Central
instance (CI) even if the central services like message and enqueue service are part
of the standalone ASCS instance type.

regards

[Former Member · Accepted solution]

Thanks Joe for the link. This is really something I was unaware of and helpful now.

So from the entire discussion what we conclude is the existence of CI along with ASCS is purely a conceptual existence which earlier was used to be the basic underlying concept of an SAP system; on practical grounds there is literally no difference between CI and DI when ASCS exists (except that the DVEBMSGxx folder remains on CI).

Regards,

Sourabh Majumdar

[Former Member · Accepted solution]

Hi Sourabh,

Valid question and good summary of the discussion. Thanks. This helps to clear the concept.

Regards,

Kunal.