z/OS system and software requirements

The VSAM Remote Source remote log reader runs in a single z/OS® address space. The recommendation is to make this address space a started task that is started as part of the IPL process so that this server is always available.

System requirements for VSAM

For replication from VSAM data sources, your system must meet the following system prerequisites and requirements:
  • IBM® z/OS Version 2.2 or later
  • CICS® Transaction Server for z/OS 5.2 or later
  • CICS VSAM Recovery (CICS VR) Version 5.1 or later is required to replicate changes made by batch jobs outside of CICS Transaction Server.

Supported VSAM data set types

Classic CDC supports capturing VSAM changes made through CICS TS file control as well as VSAM changes made in other address spaces whose VSAM access is supported by CICS VR's VSAM batch logging. VSAM clusters must specify LOGREPLICATE and LOGSTREAMID with a non-NULL value for LOG() for CICS TS logging and a non-NULL value for FRLOG() for CICS VR logging.

Replication logging can only be enabled for datasets under System Management Subsystem (SMS) control.

Other requirements include:
  • Only Key Sequenced Data Sets (KSDS) and Entry Sequenced Data Sets (ESDS) can be replicated with VSAM Remote Source. ESDS and RRDS organized data sets do not store key information in the record data and it is possible to have duplicate records that might lead to duplicate key failures at the target. Currently, the ESDS RBA and RRDS RRN cannot be replicated to the target, which might cause duplicate target records. VSAM Remote Source allows replication of ESDS data when you do not require a unique key at the target, your data provides a unique key for the target, or you use some other strategy (for example, journal control fields) to create a unique key. Both fixed- and variable-length ESDS data is allowed for both refresh and replication with the restriction that VSAM Remote Source does not provide the ESDS RBA value and you cannot depend on that for a unique key at the target.
  • Innovation Access Methods (IAM) supports replication logging for VSAM Remote Source.
  • All table mappings in the same subscription must be mapped to VSAM data sets that use the same replication log. If you change the name of the log stream defined to any one VSAM data set within a subscription, all other VSAM data sets in the same subscription must also be updated to use the same replication log stream name. Otherwise, you must move the changed VSAM data set to a new subscription.
  • A source data set cannot be opened by any address space that will be logging updates when the log position is set. This requirement is to ensure there is a tie-up record logged for the VSAM cluster to allow VSAM Remote Source to relate changes to the data set they affect.
  • The maximum RECORDSIZE that is defined for the VSAM file cannot exceed 32767 bytes.
  • The user ID associated with the job or started task needs an OMVS segment for TCP/IP access.

Load library authorization requirements

  • The load library referenced in the remote log reader address space requires authorized program facility (APF) authorization for the installation load library on the source logical partition (LPAR) where the address space executes.

TCP/IP requirements

  • The remote log reader uses TCP/IP to communicate with the capture service running in the IBM® Data Replication VSAM Remote Source container. By default, the remote log reader is configured to use port number 9087 which IANA has reserved for use by Classic. You can change this port number if desired.
  • The remote log reader must have authority to accept inbound connections, because it listens for connections from the container. You should configure your network environment to ensure only connections from the Remote VSAM source container Linux server are allowed to connect to the z/OS log reader port.
  • Communications between the remote log reader and container use unencrypted private protocols. For additional protection, a site can secure communication sessions between the remote container and its z/OS VSAM service component using AT-TLS on z/OS and a TLS proxy for the remote container.
  • You can define CDC table mappings that are used only for refresh with a refresh method. These CDC table mappings can be for VSAM data for which you do not enable change capture and can also be sequential files that act as VSAM in VSAM remote source.

z/OS log stream usage considerations

  • The remote log reader address space uses a DASD-only log stream for diagnostic logging purposes. This log stream is automatically created during the installation/customization process.
  • Each subscription requires its own replication log stream. Scripts and procedures are provided to create one of these log streams. Depending on the environment, a replication log stream can be DASD-only or will need to be hosted in the coupling facility.
  • If you are executing in a mono-plex environment, then a DASD-only log stream can be used. In a CICS Plex or data sharing environment where the VSAM files can be updated from multiple images then a coupling facility-based log stream needs to be used.
  • Some processing of the z/OS component during replication log reading is eligible for zIIP offload. Refresh processing performed by the z/OS component is not eligible for zIIP offload.

External security manager (ESM) considerations

  • The remote log reader address space uses the authorization ID associated with the address space to access all support libraries, z/OS log streams, and customer data sets. The address space needs read permission to access the subscription z/OS log streams and, during refresh, mapped VSAM data.
  • Update permission is required for the diagnostic log stream and configuration files referenced by the remote server address space and read permission is required for the APF authorized load library.

Memory requirements

  • The remote log reader address space is configured to use 256MB of 31-bit storage. This is a suitable size for most deployments. 64-bit memory objects are not used.

Clock and time zone considerations

You should confirm that your z/OS LPAR is configured with the proper time zone offsets. You can use the z/OS operator command D T to show the LPAR's current time and ensure that it is correct. VSAM remote source uses UTC timestamps for positioning in the replication log and an incorrect clock can prevent changes from replicating. For more information see Displaying the local and coordinated universal time and date (T).