Which condition would prevent an administrator from unmounting a VMFS datastore?

When a datastore belongs to a Storage DRS datastore cluster, vSphere enforces a management relationship that prevents unmounting the datastore independently, because doing so would break the datastore cluster's capacity and I/O monitoring functions. The administrator must first remove the datastore from the Storage DRS cluster before vSphere will allow the unmount operation to proceed.

vCenter Server templates on a datastore can be unregistered from the inventory prior to unmounting, and their presence alone does not create the same persistent administrative block as Storage DRS cluster membership.

A datastore being mounted by multiple hosts does not prevent unmounting - each host can independently unmount a shared VMFS datastore without affecting the other hosts.

If the storage backing a datastore is already detached, vSphere treats the datastore as inaccessible rather than enforcing an active management lock, which is a different condition from Storage DRS membership.