Request compression at the system level
You request compression at the system level by defining the storage management subsystem (SMS) with the COMPRESS options ZEDC_R (zEDC Required) or ZEDC_P (zEDC Preferred) in the IGDSMSxx member of parmlib. The data class COMPACTION value must be set to Y.
- COMPRESS({TAILORED|GENERIC|ZEDC_R|ZEDC_P})
- Specifies the type of compression to be
used for the data set.
- GENERIC
- Specifies that the data set be compressed using generic Dictionary Building Block (DBB) compression. The dictionary is derived from a defined set of compression algorithms in data set SYS1.DBBLIB.
- TAILORED
- Specifies that the data set is eligible for compression that is tailored to the data set. A
tailored dictionary is built, using the initial data written to the data set, and embedded into the
data set. The dictionary is issued to compress or expand data written to or read from the data set.
This type of compression applies only to sequential data sets, not to VSAM KSDSs.
To convert an existing DBB-based compressed data set to use tailored compressions, you must set the COMPRESS parameter to TAILORED and copy the generic DBB-based data set to a new data set that meets compression requirements.
- ZEDC_P
- Specifies that the data set be compressed using zEDC compression, as with the ZEDC_R option. But here, the system does not fail the allocation request, but rather create either a tailored compressed data set if the zEDC function is not supported by the system, or create a non-compressed extended format data set if the minimum allocation amount requirement is not met.
- ZEDC_R
- Specifies that the data set be compressed using zEnterprise® data compression (zEDC). No separate dictionary is created, as zEDC compression
hides the dictionary in the data stream. A new dictionary starts in each compression unit. The
system can decompress the segment as is.
With this option (as opposed to ZEDC_P), the system fails the allocation request if the zEDC function is not supported by the system, or if the minimum allocation amount requirement is not met.
Note:- Use tailored compression only when all systems in the SMS complex have been converted to DFSMS/MVS 1.4 or later, and when there is no need to revert to a prior release level for local recovery or remote recovery with Aggregate Backup and Recovery Support (ABARS). The date of general availability for DFSMS/MVS 1.4 was in 1997.
- To convert an existing DBB-based (generic) compressed data set to use tailored compression, or to convert from either generic or tailored to zEDC compression, first set the COMPRESS parameter to TAILORED, ZEDC_R, or ZEDC_P in the IGDSMSxx parmlib member. Use IEBGENER, ICEGENER, REPRO, or any QSAM or BSAM application to copy the data set to a new data set that meets compression requirements.
- The zEDC feature must be installed on all systems before using zEDC compression. For more information on zEDC compression, see z/OS MVS Programming: Callable Services for High-Level Languages.
Default: GENERIC
For a description of the data class COMPACTION option, see Request compression at the data set level.