A data set status information record is written to every page data set. The status record identifies the system using the data set.

The status record is validated during IPL. If the record indicates that the data set is in use by another system, message ILR030A is issued and the system waits for an operator response to allow or disallow use of the data set.

Note that this feature does not offer full protection in the case of a page data set that was defined on, or was last used by a pre-z/OS V1R3 environment. This is because the status record used to perform this check did not exist prior to V1R3. The z/OS1.3 system will format the status record, issue ILR029I as an informational message and continue to use the data set (along with the other system).

Once the IPL is complete, the status record is validated on a regular interval. If concurrent use of a data set is detected, both systems will be terminated with a 025 wait state code. Catalog information will also be validated with the status record. If the data set is deleted or key catalog information changes, the system will be terminated with a 025 wait state code.