Configuring the system logger for use in the Copy Services Manager environment

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When the system logger is used in an IBM® Copy Services Manager environment, steps must be taken to avoid data consistency issues.

The following situations can lead to data consistency issues when using Copy Services Manager with the system logger:
  • The Release I/O after Suspend option has been selected for a Metro Mirror session.
  • The system logger couple data sets (CDSs) are not part of the Metro Mirror session. In this situation, the data sets are not frozen even though the related application secondary volumes have been frozen.
  • The system logger log streams use coupling facility (CF) structures.
  • After a suspend event, the primary site fails and you must recover at the alternate site.

If the secondary disks in the Metro Mirror session are frozen and the workload continues to run using the primary disks, the data on the secondary disks is out of sync with the CF structures or the CDSs. If you attempt to restart the applications using the frozen secondary disks, the restart fails because of this inconsistency. For example, Customer Information Control System (CICS) require a cold start instead of an emergency restart, and transaction backout and handling of in-doubt transactions are not possible.

If Release I/O after Suspend has been selected for Metro Mirror sessions, the actions that are shown in Figure 1 are required.

TVT Instructions: This graphic is new for Tivoli Storage Productivity Center for Replication 4.2.1. hs_logger.cdr
Figure 1. Planned swap
This graphic illustrates a planned swap.
  1. In the system logger policy, all CF log streams must be forced to duplex to staging data sets. The following data sets must be in the same Metro Mirror session:
    • Log stream staging data sets that are direct access storage device (DASD)-only
    • CF log stream data sets
    • All of the offload data sets for both types of log streams
  2. Four system logger CDSs must be set up as follows:
    • The primary system logger CDS in Site 1 must be in the same Metro Mirror session.
    • The spare system logger CDS in Site 1 must not be in a Metro Mirror session.
    • The alternate system logger CDS in Site 2 must not be in a Metro Mirror session.
    • The spare system logger CDS in Site 2 must not be in a Metro Mirror session.

Set up all CDS types other than the system logger CDSs as required for Copy Services Manager. That is, the primary system logger CDS should be in Site 1 and the alternate system logger CDS in Site 2. There should be spare CDSs in both sites. The alternate and spare CDSs should be not be in a Metro Mirror session.

By following the preceding steps, the primary system logger CDS, CF log stream staging, and offload data sets are on volumes in the Metro Mirror session. If a freeze occurs, system logger data will be consistent on the secondary devices. If the reason for the freeze requires that you restart from the secondary devices, you can recover and use this frozen copy of the system logger environment.

Important: Ensure that no CF log streams remain allocated in any coupling facilities that the production systems have access to following a disaster. In this situation, recovery occurs from the mirrored copies of the data. If any log streams are allocated, you must force the connections and ensure the structure is deleted before restarting your production systems.