The ARCMMEXT installation exit receives control when a process, including command migration of a single data set, selects to migrate an already migrated data set.

This exit is called for both system- and non-system-managed data sets that are eligible to migrate from a migration volume. A flag in the MCD record (MCDSMSFG) is passed to the exit indicating whether the data set is system-managed. Contrast this exit with the ARCMDEXT, which is used when data sets are migrated from a level 0 (user) volume.

Parameters passed to ARCMMEXT can be located above or below the 16 MB line and have 31-bit or 24-bit addresses. In order to handle both cases, the ARCMMEXT should be link-edited with AMODE 31.