What makes a namespace fault tolerant is where and how the root is hosted. For a stand-alone namespace to be fault tolerant,the root must be created on a server cluster. For a domain-based namespace to be fault tolerant,you need at least two domain controllers in the domain (to provide referrals to the namespace) and two namespace servers hosting the root (to provide referrals to folder targets). This last point about domain-based namespaces is often misunderstood,too. Customers think that because the namespace is in Active Directory,this somehow makes the namespace fault tolerant. The AD aspect is more about consistency than redundancy. All namespace servers will poll a domain controller periodically to obtain the latest DFS Metadata,helping ensure that all the namespace servers provide referrals that are consistent. You still need an operational domain controller and namespace server (which can be the same server) to provide referrals.