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z/OS DFSMS Using Data Sets
Beginning with z/OS Version 2, z/OS supports two formats of PDSEs: version 1 and version 2. Version 2 PDSEs, introduced in z/OS Version 2, take advantage of a number of internal design changes to improve space utilization in the data set, reduce CPU processing and I/O, and provide better index searches. They also support generations for members, as described in PDSE Member Generations. All PDSEs created before z/OS Version 2 are by definition version 1 PDSEs, and Version 1 remains the default for newly allocated PDSEs. To create a version 2 PDSE, specify DSNTYPE=(LIBRARY,2) on the DD statement or the equivalent on the TSO ALLOCATE command or dynamic allocation. Alternatively, the system programmer can specify the PDSE_VERSION keyword in a IGDSMSxx member of SYS1.PARMLIB. Outwardly, version 1 and 2 PDSEs appear the same; and they present no external changes to the user.
Version 2 PDSEs can only be created on z/OS Version 2 systems; they can be read and written to on previous releases of z/OS, but cannot be allocated there.
The goal of version 2 PDSEs is to provide improved PDSE performance overall. There is one situation where an application might perform better with a version 1 PDSE (this situation is not considered likely):
You can do the following to specify the version for new PDSE data set allocations:
Note: PDS remains the default value for DSNTYPE even if PDSE_VERSION is specified in the IGDSMSxx member.
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