Questions regarding vplex data migration

1. In "Move data within cluster" wizad, the local device can do 'device migration' and 'extent migration', the distributed devices can only do 'extent migration', why?

2. In "Move data across clusters" wizad, i can not find any device can be migrated, why ?

For local device across clusters migration, Does 'global visible' volume attribute must be set first before it can be migrated ?

For distributed devices, can i migrate one mirror leg from one cluster to another cluster, so two legs are in the same cluster finally ?

3. Can i remove one mirror leg from the distributed devices ? If can, will 'global visible' attribute be continue to maintain on the corresponding virtual volumes, so the hosts in both clusters still have the volume access after cutting one leg?