Data integrity considerations

In some circumstances, DFSMSdss can detect and correct inconsistencies while processing data. For example, DFSMSdss checks to verify the reliability of a partitioned data set (PDS) directory before it uses the PDS. You can also use the CHECKVTOC keyword to instruct DFSMSdss to perform additional consistency checking on the VTOC before data processing begins on that volume.

If you are creating backups as part of disaster recovery preparedness, you may want to take additional steps to ensure the validity of that data. You can establish validity before you invoke DFSMSdss, or as part of the DFSMSdss invocation.

Note: Periodically running the Access Method Services DIAGNOSE function to reorganize VSAM data sets establishes validity before you invoke DFSMSdss. However, not specifying the NOPACK keyword establishes validity as part of the DFSMSdss invocation. In this case, DFSMSdss verifies the PDS directory. If you specify the CHECKVTOC keyword, DFSMSdss performs consistency checking on the VTOC.

The choice between logical and physical processing depends on the expected type of abnormal condition (if any). Neither processing mode provides a significantly higher level of data integrity. Logical processing and physical processing are simply different views of the same data. One mode could detect a condition that the other mode would miss. For example, a frequent PDS abnormal condition that does not cause problems during physical processing might cause problems during logical processing. On average, the selected DFSMSdss processing mode should closely mirror the mode in which you typically access data. Generally, logical processing is the most applicable choice.