Using "system controller replace" Commands to Upgrade Controller Hardware Running ONTAP 9.8
This guide describes how to upgrade the controller hardware without disruption.
You can nondisruptively upgrade the controller hardware on a pair of nodes running ONTAP 9.8 by migrating non-root aggregates from the original nodes to the new nodes in the same cluster. The data hosted on the nodes that are being upgraded is accessible during the upgrade.
This procedure uses a method called aggregate relocation (ARL), which takes advantage of the HA configuration to enable you to move ownership of non-root aggregates from one node to another if they share storage within the same cluster.