Allocating VSAM data sets

To define Virtual Storage Access Method (VSAM) data sets, use the z/OS® AMS DEFINE CLUSTER command.

VSAM database data sets are defined by an AMS DEFINE CLUSTER command.

Related reading: This command and all its parameters are described in z/OS DFSMS Access Method Services for Catalogs.

Sharing of VSAM data sets is specified by the DEFINE CLUSTER SHAREOPTIONS keyword. IMS VSAM databases that use data sharing must be defined with at least SHAREOPTIONS (3,3). This allows IMS to access the VSAM VSI so that any extensions to the VSAM data set are known by all IMS sharing systems.

VSAM data sets opened for update by XRF-capable IMS online systems must also use at least SHAREOPTIONS (3,3), in order for extensions to the VSAM data set to be tracked by the alternate system. Because VSAM data sets opened for input are not extended by VSAM, the VSAM VSI is not required. SHAREOPTIONS (3,3) can be used even if the online system is XRF capable. SHAREOPTIONS (3,3) is not necessary for Fast Path DEDBs; SHAREOPTIONS (2,3) can be used for this environment.

You can enable VSAM data sets to use extended address volumes (EAVs) that are available in z/OS V1.12 or later. To enable a VSAM data set to use EAVs, specify an EAV volume on the VOLSER parameter when you allocate the data set. In addition, you can specify the attribute EATTR to indicate whether the data set supports extended attributes.