WHY THE USER CATALOG CANNOT BE IN THE SAME DEVICE AS ACF2 DB?

Document ID : KB000076548
Last Modified Date : 05/04/2018
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Question:
Why can't I have the ACF2 databases on the same volume as the user catalog? 
Answer:

The ACF2 databases are occasionally closed and opened by acf2 processing and this would require access to the catalog

If database and catalog are on the same volume, there would be a reserve on the volume and so the catalog would not be
accessible. This would cause a deadly embrace - and an IPL will be needed.