What do anti-affinity rules do in VMware vSphere?

Anti-affinity rules in VMware vSphere are designed to ensure that specified virtual machines (VMs) do not run on the same ESXi host. This capability is crucial for high availability and fault tolerance. By implementing anti-affinity rules, administrators can separate critical workloads across different hosts, reducing the risk of a single point of failure.

For instance, in a scenario where certain VMs provide different components of an application, keeping them on separate hosts ensures that if one host fails, the other components remain operational on different hosts. This separation can help maintain service availability and minimize downtime.

The other options would either indicate a behavior where VMs would be placed together on a single host, which is contrary to the purpose of anti-affinity rules, or describe functionalities not related to VM placement policies, such as resource allocation or backup processes.