Locating CASs

Once you have decided where to install CMASs and how to link them, you can turn your attention to the CASs.

Where CASs are required

The rules and recommendations on where to locate a CAS are:

Figure 9. Valid CAS configurations. The most likely configuration is that shown on System A. However, those shown on System B and System C are also valid. CICSPlex SM data cannot be accessed from System B because there is no MVS/TSO instance. However, because CAS2 has links to other CASs on MVS images where MVS/TSO is available, the data on System B is accessible from other MVS images. System C has no CMAS, but can still be used as an access point for CICSPlex SM data on other MVS images.
The diagram shows three systems, System A, System B and System C. System A has a CAS, CAS1, a CMAS, CMAS1 and has MVS/TSO with ISPF. System B has a CAS, CAS2 and a CMAS,CMAS2. System C has a CAS, CAS3 and has MVS/TSO with ISPF. There are direct bidirectional links between CAS1 and CAS2, CAS2 and CAS3 and CMAS1 and CMAS2.

Start of changeIt’s very easy to update the example map by applying these rules: there are five CMASs, so there must be five CASs, one on each of the MVS images on which a CMAS is installed. Figure 10 shows the addition of the CASs..End of change

CAS-to-CAS links

If you define no CAS-to-CAS links, the CICSPlex SM operator can sign on to CICSPlex SM via CAS 1 (or CAS 2, or CAS 3) and still have a complete view of the CICS systems and resources in CICSplex 1 because the CMASs managing CICSplex 1 are linked to each other. The same observation is true of CICSplex 2. For example, a CICSPlex SM operator accessing CICSPlex SM via CAS 5 can see data for TOR 3 via the links between CMAS 4 and CMAS 5. However, for both performance and availability reasons, it is better to establish links between CASs also.

Start of changeFigure 10. Adding CASs to the example map. A CAS has been added to every MVS image to which a CMAS has been assigned.
The map shows the following systems: System A is an OS/390 2.10 system with a CICS Transaction Server for OS/390, Version 1 Release 3 TOR and two CICS Transaction Server for OS/390, Version 1 Release 3 AORs. System B is an OS/390 2.10 system with a CICS Transaction Server for OS/390, Version 1 Release 3 TOR, a CICS Transaction Server for OS/390, Version 1 Release 3 AOR and a CICS Transaction Server for OS/390, Version 1 Release 3 FOR. System C is a z/OS/ 1.4 system with two CICS Transaction Server for OS/390 Release 2.3 AORs. System D is an OS/400 3.1 system with two CICS/400 3.1 regions. System E is an OS/390 version 2 release 10 system with two CICS Transaction Server for OS/390 Release 2.2 AORs and a CICS Transaction Server for OS/390 Release 1.3 AOR. System F is a z/OS 1.2 system with two CICS Transaction Server for z/OS, Version 2 Release 3 AORs. The CICS regions from System A, System B and System C belong to CICSplex 1. The CICS regions from System E, and System F belong to CICSplex 2. The CICS regions from System D do not form part of a CICSplex. CAS 1 and CMAS 1 are installed on System A. CAS 2 and CMAS 2 are installed on system B. CAS 3 and CMAS 3 are installed on System C. CAS 4 and CMAS 4 are installed on system E. CAS 5 and CMAS 5 are installed on System G. CMAS 3 and CMAS 5 are both maintenance point CMASs. CMAS 3 also has access to NetView. CICSplex 1 has bi-directional links between CMAS1 and CMAS2 and CMAS2 and CMAS3 and a bi-directional link between CMAS1 and CMAS3. CICSplex 2 has a bi-directional link between CMAS4 and CMAS5.
End of change

A second consideration in the example is the availability of a single point of control for the enterprise. If you add no CAS-to-CAS links, a CICSPlex SM operator cannot see CICSPlex SM data for CICSplex 2 from MVS image 3, for example. This arrangement might be suitable in some enterprises (indeed, it might be the reason why it was decided to have multiple CICSplexes in the first place). However, if you do want a single point of control for the enterprise and have multiple CICSplexes, CAS-to-CAS links are required.

Thus, CAS-to-CAS links can provide a single point of control for the enterprise by allowing the CICSPlex SM operator access to CMASs that may not be even indirectly connected to each other; CMAS-to-CMAS links provide an SSI for all MASs that connect to those CMASs; and CICSPlex SM exploits a combination of CAS-to-CAS links and CMAS-to-CMAS links to give the best possible performance.

In the example, few CAS-to-CAS links are essential. If you add two links, one from CAS 1 to CAS 4, and one from CAS 4 to CAS 1, both CAS 1 and CAS 4 can function as an single point of control because each has access to data about CICSplexes 1 and 2. However, for maximum performance and availability, and because the total number of CASs in the enterprise is small, you are going to link every CAS to every other CAS. As with the CMAS-to-CMAS links, the formula for calculating the number of links to be defined is n2 - n, where n is the number of CASs. In the example, there are five CASs, and so 20 links must be defined to establish full connectivity for the enterprise. If you have room on your map, add the CAS-to-CAS links. As the example map is beginning to look crowded, the CAS-to-CAS links are listed separately in Table 2.

Table 2. CAS-to-CAS links required for full connectivity among the example CASs
CAS 1 to: CAS 2 to: CAS 3 to: CAS 4 to: CAS 5 to:
CAS2 CAS1 CAS1 CAS1 CAS1
CAS3 CAS3 CAS2 CAS2 CAS2
CAS4 CAS4 CAS4 CAS3 CAS3
CAS5 CAS5 CAS5 CAS5 CAS4

Full connectivity among the enterprise CASs is recommended for performance and availability reasons. However, it is not essential: if the enterprise CMASs are adequately connected to each other, a single point of control for the enterprise can be established without full connectivity among the CASs.

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