MIM not protecting an allocated PDSE when running DFDSS defrag

Products

• MIM Resource Sharing (MIM)
• MIM Data Sharing (MII)

Issue/Introduction

This is regarding a DEFRAG - PDSE ENQ issue that was encountered. 

• You ran a DFDSS DEFRAG on a PDSE residing on your Test Plex. It affected the PDSE on our PROD plex.
• The LPARs are not in the same SYSPLEX but DASD is shared between different SYSPLEX/LPARs.
• When a file is in-use, DFDSS Defrag operation should skip the allocated file, but that did not happen with the PDSE in question.
• MIM is in place in your system and is used for sharing the resources across the LPARs and SYSPLEXes.
  
  

What is the reason for such an unexpected scenario,  and are any changes required for MIM?

 

Resolution

The MIM documentation has a section about PDSE Type Data Set Considerations.

Near the beginning of that section there is a warning:
Attempts to share PDSEs across sysplex boundaries may result in data integrity exposures, corrupted PDSEs, or loss of data.

Review of this section is recommended.

The subsection on Integrity Exposures explains specifically why the exposures occur and that this is an IBM limitation, not one over which MIM has any control or influence.

This is not a MIM problem.

Additional Information

The IBM z/OS DFSMS Using Data Sets manual provides additional information.
In the subsection titled "Multiple System Sharing of PDSEs" it specifically states

Note: PDSE sharing between sysplexes is not supported.