Coupling facility connection failures

Various types of problems can cause the connection between IMS and the coupling facility to be lost. For example, the connection is lost if the physical link (a fiber optic cable) is cut, after power failures, hardware check stops, coupling facility microcode failures, and similar events.

If there are multiple links between an IMS and the coupling facility, loss of one link has no effect on IMS or the IRLM. However, if the link that is lost is the last link, it must be recovered before data sharing on that IMS can be restarted. Processing still continues for all other IMS systems in the data-sharing group.

When the last connection between IMS and the coupling facility is lost:

  • If the connection was between an IMS and an OSAM or VSAM structure, IMS drops out of data sharing. Any transactions trying to access shared data terminate with a U3303 abend. However, transactions accessing nonshared databases can still be processed.
  • If the connection that failed was between an IRLM and the IRLM lock structure, the IRLM disconnects from the data-sharing group. Any transactions trying to access shared data terminate with a U3303 abend.

When connection between the coupling facility and IMS is reestablished, z/OS® notifies IMS and IMS resumes data sharing.

The following figure shows the connection loss between IMS, OSAM, and VSAM structures as a result of a coupling facility connection failure.

Figure 1. Connection loss between IMS and OSAM and VSAM structures
begin figure description - This figure is described in the surrounding text. end figure description.

The connection that is lost is the link between the MVS2 and coupling facility CF02. When the last link fails:

  • IMS2 drops out of data sharing and only nonshared databases can be accessed on the MVS2 system. IMS1 and IMS3 continue data sharing.
  • Transactions trying to access shared data on MVS2 terminate with a U3303 abend.

In this circumstance, you receive the DATA SHARING STOPPED message. You can enter the z/OS DISPLAY XCF,STRUCTURE,STRNAME= command to determine what failed. The displayed output, as shown in the following example, shows that the MVS2 link to the coupling facility failed. MVS1 and MVS3 links are still active.

11:44:37.84 D XCF,STRUCTURE,STRNAME=OSAMSESXI
 
             ⋮
 
             & AMPERSAND DENOTES CONNECTOR WHO LOST CONNECTIVITY TO STRUCTURE
             CONNECTION NAME  ID VERSION  SYSNAME  JOBNAME  ASID STATE
             ---------------- -- -------- -------- -------- ------------
             IMS1             03 0003000D MVS1     DLIOCSA8 0066 ACTIVE
            &IMS2             01 0001001D MVS2     DLIOCSB8 0066 FAILING
             IMS3             02 00020014 MVS3     DLIOCSC8 0066 ACTIVE

In the online environment, the MVS2 link to the OSAM structure is reestablished, MVS notifies IMS, and data sharing resumes. In the batch environment, you need to resubmit the batch job when the link is reestablished. You will receive the CF INITIALIZATION COMPLETE message, indicating IMS has resumed data sharing. If you issue a DISPLAY XCF,STRUCTURE command, display output shows that MVS2 is connected (ACTIVE).