For SMB3 transparent failover to perform efficiently, the Service Witness Protocol must be configured.
The Service Witness Protocol enables a registered client to receive notification of any state changes on a continuously available server. For example, if a continuously available SMB server provides SMB shares to a Hyper-V server, the protocol enables the Hyper-V server to receive notification of any state changes without needing to wait for the connection to time out. This ensures that there is a fast notification and recovery time from an unplanned failure, such as a network loss.
When a client connects to an SMB share, the client has to identify and then register with the witness EVS to receive witness event notifications. If the client cannot identify or register with the witness EVS, the NAS server cannot provide witness notifications to that client and standard timeouts will apply.