DASD management considerations
If you use a DASD management program to create backup copies of data for disaster recovery purposes or merely to move data sets between MVS systems, the non-VSAM and the VSAM components must be running on both the target and destination MVS systems to expand the compressed data.
Most commercial DASD management programs, such as IBM DF/DSS, Innovation FDR, or Computer Associates CA-FAVER, move data in physical mode using EXCP processing, creating a bit image copy of the data just as it resides on the DASD. Because of the EXCP processing, DATA ACCELERATOR Compression is not invoked and does not compress or expand data during the backup, restore, or copy operations of any of these products. If the data was originally compressed, it will remain compressed during the backup, restore, or copy operations. If the data was not compressed originally, DATA ACCELERATOR Compression cannot be invoked to compress the data during the backup, restore, or copy operations.
Even though DATA ACCELERATOR Compression discovers programs that use EXCP or other unsupported access methods through its auto registration process, you should register these programs for the Bypass Compression option set to YES to reduce overhead associated with auto registration and exception processing.
If you use programs that perform a BSAM or QSAM I/O request (such as IEBGENER or IDCAMS) to create backup copies of the data, the non-VSAM and VSAM components are invoked to allow data compression and expansion. These programs can create backup copies in expanded format of compressed data for MVS systems that do not have the DATA ACCELERATOR Compression product. IEBGENER and IDCAMS can back up data in expanded format because they use an access method supported by DATA ACCELERATOR Compression. DATA ACCELERATOR Compression expands compressed data for input operations and compresses data for these programs' output operations if the data sets are designated for compression. Do not set the Bypass Compression option to YES for these utilities. Setting this option to YES prevents copying compressed data into expanded data sets or from compressing expanded data sets. Use these programs to make a copy of compressed data residing on a system without DATA ACCELERATOR Compression.
You may want to use programs that employ access methods and techniques supported by DATA ACCELERATOR Compression, such as IDCAMS and IEBGENER, to perform backup, restore, copy, or move operations only. If you do not perform other actions on the data, and the source and destination attributes are kept identical (for example, compressed to compressed), a front-end program can be generated that uses the Bypass Compression option to exempt the program from expanding the data on input and compressing the data on output. This practice avoids compression and expansion overhead and reduces CPU and job run time. For more information about creating an IDCAMS front-end, see BMC Software Subsystem.
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