The alert for Protection Policy PP-BCA-1HR indicating critical availability issues is most likely due to the workloads included in the policy no longer meeting their intended Recovery Point Objective (RPO). A 1-hour snapshot frequency implies a stringent RPO, which if not maintained, could result in data loss beyond acceptable business limits. This scenario typically generates a critical alert in Prism Central, especially when the snapshots required to meet the RPO are not completed as scheduled due to any number of issues such as resource constraints or network issues.References: Nutanix Prism User Guide, Nutanix Data Protection Best Practices.

The error encountered during the LCM inventory process, which mentions "Could not find a module for entity with reference name nutanix.ncc.update," typically indicates that the cluster has not yet been licensed. The Life Cycle Management (LCM) functionality in Nutanix systems requires a valid license to perform operations such as inventory checks and updates. Without this license, LCM cannot retrieve or update the necessary software modules, leading to the stated error. Licensing the cluster would resolve this issue and allow the LCM processes to proceed normally.References: Nutanix LCM Documentation, Nutanix Licensing Guidelines.

Explanation
Ref:https://next.nutanix.com/community-blog-40/scaling-up-vm-storage-performance-on-ahv-volume-group-loa

Ref:
https://portal.nutanix.com/page/documents/solutions/details?targetId=BP-2005_Data_Protection:BP-2005_Data_

Given the constraint of a 16-port switch for a 20-node cluster, the consultant cannot physically connect all nodes to the network simultaneously. VLAN tagging allows multiple virtual networks to be carried over the same physical network. However, the challenge here is not about VLANs but the physical limitation of ports.
The practical approach would be to manually create the cluster, potentially in stages, as the full network capacity required for all nodes is not available.References:
* Nutanix University - NCS-Core 6.8 Learning Path
* The Nutanix Bible, Networking chapter (https://www.nutanixbible.com/)