CMMVC9684E A VDisk cannot be shrunk if it is the target of a FlashCopy® mapping.

Explanation

A volume cannot be shrunk if it is the target of a FlashCopy mapping. If the volume is a source of a FlashCopy mapping, it can be shrunk provided no FlashCopy mapping for which it is the source has a starting capacity that is greater than the proposed size of the volume. The starting capacity can be found in the lsfcmap view.