1. A method comprising: receiving at a network storage server, from a backup client, a request identifying a particular file to be restored from a block-level backup set of a data set that contains a plurality of files; and restoring the file from the block-level backup set at the network storage server by using a client-server backup protocol, without restoring the entire data set from the backup set, wherein restoring the file from the backup set includes using a first backup image in the backup set, at the network storage server; and in response to a determination at the network storage server that a second backup image in the backup set is needed to continue restoration of the file, automatically suspending restoration of the file and sending a request for the backup client to change from the first backup image to the second backup image, from the storage server to the backup client.