Migration considerations for DATA ACCELERATOR Compression

To ensure that DATA ACCELERATOR Compression functions properly and can coexist with other products at your site, review the migration considerations in the following table:


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ConsiderationDiscussion
Engine Level Mask migration
With each new release, the Engine Level Mask (ELM) value is likely to change. The ELM represents the level of the compression engines and is specified in the Commands data set.

Because the ELM is backwards compatible, the latest value supports all previous engine levels. This compatibility facilitates easy migration from one release to the next. However, data sets that are compressed with one ELM value might not be able to be expanded by a product that uses an earlier value. This consideration is important if it is necessary to fallback to an earlier release.

We recommend that you not change the ELM value when migrating to the current release. This practice helps ensure compatibility with compressed data sets if you decide to revert to an earlier release. When you have determined that you will always run the latest release, change the ELM value to the highest value available.

For changes in the default ELM of this release, see the applicable release notes.

Fallback considerations
Review the material about the Engine Level Mask (ELM) before you decide to start an earlier version of DATA ACCELERATOR Compression on your system. Do not revert to an earlier version of DATA ACCELERATOR Compression if the ELM values would create an incompatibility.
Implementation of a new release
For most new releases of DATA ACCELERATOR Compression, implementing the release requires following the installation procedures, refreshing the MVS linklist libraries, and starting the subsystems. No IPL is required.

However, some changes to DATA ACCELERATOR Compression or subsystem modules can require an IPL. For more information about required IPLs, see the applicable release notes.

REGISET migration
The REGISET data sets are compatible from one release to the next. If DATA ACCELERATOR Compression attempts access to a REGISET that has an obsolete format, the product updates the REGISET format.

If you need to make a copy of the REGISET for a stand-alone system, we recommend using the BMC EXTRACT utility to create a copy of the REGISET; then, use IDCAMS REPRO to copy this extracted data into the new REGISET.

REGISET sharing
DATA ACCELERATOR Compression 1.2.02 changed the way in which serialization is handled for the REGISET. Consequently, DATA ACCELERATOR Compression 1.2.02 and later cannot share the REGISET with earlier releases.

For REGISET sharing compatibility, ensure that all releases of DATA ACCELERATOR Compression that share a REGISET are at a compatible level (all releases at version 1.2.02 and later, or all releases at a version earlier than 1.2.02).

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