I had to migrate online a very critical production storage running on FAS8040 with DS2246 disk shelves to FAS8200 with DS224 disk shelves. It was running and Ontap 9.3 cluster with two nodes and was serving high load NFS to Linux servers running SAP HANA and other SAP services.
This migration was done online successfully by loaning two CN1610 cluster switches. Summary of this procedure is given
1. Convert two node switchless cluster to switched cluster.
2. expand cluster to a four node cluster by adding two new FAS8200 controller.
3. Create storage aggregates, ifgroups on new FAS8200 cluster.
4. Did volume move from FAS8040 aggregates to FAS8200 aggegates.
5. Switch home node and home port of LIFs from FAS8040 nodes to FAS8200 nodes.
6. Make sure that all resources except node specific LIFs like cluster LIFs of these nodes, node management LIFs are evacuated from FAS8040 nodes.
7. Remove FAS8040 nodes from the cluster.
8. Convert switched cluster back to switchless cluster.
This is not a case of head swap alone, but we are replacing both controller and disk shelves.
This is a case of seamless online migration, where I replaced Netapp hardware (both controller and disk shelves), which was reaching end of support (FAS 8040 controller, DS2246 disk shelves) with new hardware (FAS 8200 controller, DS224 disk shelves).