Q: Why are affinity rules important in vSphere Storage DRS?

A:In VMware vSphere's traditional DRS, affinity rules provide a way to define whether virtual machines (VMs) should, or shouldn't, be collocated on thesame host as the result of load balancing. These rules ensure, for example, that your two domain controllers (DCs) never end up on the same host, orthat two servers requiring high network connectivity always end up together.

Unlike traditional DRS, Storage DRS concerns itself with VM disk files. Affinity rules in Storage DRS can be used to ensure a VM's disk files arealways migrated with each other (or are always on different volumes). They can also ensure that the disk files of two separate VMs end up together orsegregated as a result of load balancing. If your vSphere environment runs VMs with any of these use cases, you'll want to configure one or moreaffinity rules to ensure their disk files always (or never) stay together.