SAN Volume Controller / Storwize / Flash System version 8.4.2 allows you to non-disruptively migrate a LUN between array controller clusters. It’s set up like remote copy, except you can map the remote copy to the same host at the same time. The remote copy becomes non-preferred paths for the same vdisk and vdisk ID. Then you can switch who is primary. Then you can remove the old copy.

Here is someone who did a demo video: https://www.youtube.com/watch?v=NpcOoshkm4w​