Executing an intra-series Hardware Non-Disruptive Upgrade (HWNDU) from a FlashArray//XR3 to an //XR4 is a highly orchestrated procedure. It involves failing over active I/O responsibilities, physically removing legacy controller nodes, and seamlessly introducing newer generation hardware without causing any downtime for the connected hosts.
Before an Implementation Engineer physically unplugs or removes a secondary controller-or initiates a failover to take the primary controller offline-it is an absolute prerequisite to verify that the frontend host multi-pathing is healthy. If a host is accidentally single-pathed to the controller that is about to be removed, an all-paths-down (APD) event will occur, causing immediate application disruption.
To safely validate this from the array's perspective, the engineer must execute the iobalance --sampletime 30 command within the Purity CLI. This specialized diagnostic command forces the array to actively sample and monitor the incoming SCSI/NVMe read and write commands across all frontend target ports for a continuous
30-second window. The output produces a detailed matrix showing exactly how traffic is distributed across both controllers and all active host initiators. If the data confirms that I/O is cleanly balanced and redundantly flowing across the surviving controller's paths, the engineer can confidently proceed with the physical removal phase of the HWNDU.