Sequential data sets can be moved from online storage to tape and recataloged by either explicit or implicit reference. Each DASD data set migrated is written as a standard labeled tape data set and cataloged, enabling any job that formerly referenced the data set through the catalog to continue to do so without change. Exception cases are those sequential data sets that are concatenated to other DASD data sets when read. This will cause an unlike device type error at allocation time. Similarly, if all generations of a GDG are to be read in by referencing the index name only, all of the generations must reside on either DASD or tape, but not mixed.
An attempt is made to catalog all data sets written to tape. Uncataloged non-GDG data sets are cataloged, and previously cataloged data sets (correctly cataloged) are recataloged. If a GDG data set is not in the catalog, no attempt is made to catalog it because VSAM catalogs will uncatalog the oldest generation when the index is full. (See NOEMPTY parameter for the DEFINE GENERATIONDATAGROUP command in IBM's Access Method Services guide.)
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