When a zone is modified by an UPDATE operation, the server must commit the change to nonvolatile storage before sending a response to the requestor or answering any queries or transfers for the modified zone. It is reasonable for a server to store only the update records as long as a system reboot or power failure will cause these update records to be incorporated into the zone the next time the server is started. It is also reasonable for the server to copy the entire modified zone to nonvolatile storage after each update operation, though this would have suboptimal performance for large zones.