What is required to ensure all VMs have the necessary resources during a host failure?

To ensure that all virtual machines (VMs) have the necessary resources during a host failure, enabling High Availability (HA) Reservation is crucial. This feature in virtualization platforms like Nutanix is designed to prevent resource contention which could occur when one or more hosts become unavailable. By enabling HA Reservation, the system reserves the necessary compute and memory resources to ensure that VMs can be restarted on other hosts in the cluster in the event of a failure. This configuration allows for a more reliable failover process, ensuring that VMs can continue to operate with the resources they require.

The other options, while potentially beneficial in different contexts, do not directly address the need for resource availability in the scenario of a host failure. Increasing CPU allocations might temporarily provide more resources to VMs, but it doesn't guarantee that those resources will be available if a host goes down. Setting up additional hosts can improve overall cluster capacity, but without HA Reservation, there is no guaranteed resource allocation for failed VMs. Finally, removing idle VMs may free up resources but isn't a reliable strategy to ensure that the necessary resources are available when a host failure occurs. The best approach to ensure resource availability during such events is through the proactive use of HA Reservation.