A method for migrating files including receiving, from a client, a first FS operation request for a target FS, making a first determination that migration for a source FS is not complete and making a second determination that the first FS operation request specifies a directory and that a directory level attribute for the directory on the target FS specifies that the directory on the target FS is un-migrated. In response to the first and second determination obtaining, from the source FS, meta-data for content in the directory and creating, using the meta-data, a directory entry for a file in the directory on the target FS. The method further includes creating an on-disk space map for the file, creating an in-memory space map for the file, and servicing, after creating the on-disk space map and in-memory space map, the first FS operation request using the target FS.