After putting a host into maintenance mode, what should an administrator do if the host does not enter maintenance mode?

When a host is placed into maintenance mode, the primary goal is to ensure that all virtual machines running on that host are either shut down or migrated to other hosts in the cluster, allowing for the safe maintenance of the hardware without impacting the virtual infrastructure. If the host does not enter maintenance mode as expected, one of the most effective steps an administrator can take is to migrate the virtual machines using vSphere vMotion.

By using vSphere vMotion, the administrator can move the active virtual machines off the host that is being placed into maintenance mode. This process helps in freeing the host from any running workloads, thus enabling it to enter maintenance mode successfully. vMotion is specifically designed to perform this live migration of virtual machines without downtime, thereby ensuring that services remain uninterrupted.

The other options, while potentially relevant in different contexts, do not directly address the immediate issue of the host not entering maintenance mode. Checking resource allocation settings might help in understanding overall capacity but does not facilitate the movement of VMs. Enabling vSphere HA admission control is more about managing HA resources and isn't necessarily related to entering maintenance mode, and scheduling DRS to run again might redistribute workloads but does not stimulate immediate migration as effectively as vMotion does.