When should the Implementation Engineer run start_ndu controller-ndu to set the HWNDU tunable?

This scenario reinforces the standard Pure Storage controller replacement methodology during an inter-generational Hardware NDU. The start_ndu controller-ndu script is a specialized internal tool explicitly designed to adjust system-level tunables on a newly inserted controller so that it can seamlessly integrate with a peer controller of a different hardware footprint (e.g., an //XR3 peer and an //XR4 or //XR5 new controller).

The Implementation Engineer must run this script before initializing CT0 (or CT1, depending on which side is currently being replaced). The exact required workflow dictates that the Purity operating system must first be installed onto the new controller's internal boot drives so the OS is present to modify. Once installed, the tunable script is executed from the command line.

Only after these HWNDU tunables are safely set can the engineer proceed to initialize the controller using puresetup, allowing it to sync its NVRAM securely and establish High Availability (HA) with the older surviving node. Attempting to initialize the controller before setting this tunable will cause the cluster's health checks to fail and reject the mismatched node, stalling the upgrade process.