The Nutanix upgrade process for software like AHV is a rolling, sequential operation designed to be non-disruptive. The Life Cycle Manager (LCM) orchestrates this process by placing only one node into maintenance mode at a time. It live-migrates the virtual machines from that node, performs the upgrade, restarts the node, and verifies its health before bringing it back into the cluster. Only after the first node has successfully rejoined the cluster does the process begin on the next node. This one-at-a-time method ensures the cluster maintains its data redundancy and availability throughout the entire upgrade procedure.

B. 2: Placing two nodes in maintenance mode simultaneously in an RF3 cluster would leave the cluster with no further fault tolerance, a risk the automated process avoids.

C. 3: This is incorrect. Placing three nodes into maintenance mode in an RF3 cluster would cause data to become unavailable, as all three replicas of some data blocks would be offline.

D. 4: This would far exceed the cluster's fault tolerance capabilities (two-node failure for RF3) and would result in significant data unavailability.

3. References

1. Nutanix Prism Web Console Guide (AOS 6.5): In the "Software and Firmware Updates" section, the 1-Click Upgrade process is described. It states, "The upgrade process is non-disruptive. The process upgrades one node at a time in a rolling fashion through the cluster." This confirms the sequential, one-node-at-a-time nature of the operation. (Reference: Prism Web Console Guide v6.5, Chapter: Life Cycle Management, Section: Software and Firmware Updates).

2. Nutanix Life Cycle Manager (LCM) Guide (v2.5): This guide details the LCM workflow. In the "LCM Update Process" section, it outlines the sequential steps for updating a node: "LCM selects a node in the cluster... puts the Controller VM in maintenance mode... puts the host in maintenance mode... performs the update... brings the host out of maintenance mode... brings the CVM out of maintenance mode... LCM moves to the next node." This explicitly confirms the one-by-one process. (Reference: Life Cycle Manager Guide v2.5, Chapter: LCM Updates, Section: LCM Update Process).

3. Nutanix University - Nutanix Hybrid Cloud Fundamentals Courseware: The course material on cluster maintenance and upgrades emphasizes that automated procedures like 1-click upgrades are "rolling upgrades." This industry term implies a sequential, node-by-node process to prevent service interruption and maintain the cluster's high availability characteristics. (Reference: Nutanix Hybrid Cloud Fundamentals, Module: Acropolis Platform Management, Lesson: Upgrading a Nutanix Cluster).