ID management for a network attached storage system using layered ID mapping virtualization. When a connection request is received at a NAS server, it is determined whether the request is for a new user, and if so, user IDs are created for the new user. External user ID and filesystem user ID are mapped to the internal user ID, and user ID is verified at the NAS server kernel on subsequent logins with an external database. The user IDs are remapped for the changed user account, and updated mappings are transmitted from the NAS server to one or more NAS server kernel repositories.