1. In a network file server in which a plurality of data mover computers share access to storage and service file access requests from network clients, a method of sharing read access and write access to a file in the storage, a primary one of the data mover computers having primary responsibility for control of access to the file and a secondary one of the data mover computers having secondary responsibility for control of access to the file, said method comprising: the secondary data mover computer receiving a request from a first network client for read access to the file; and then the secondary data mover computer responding to the request from the first network client for read access to the file by requesting a read lock on the entire file from the primary data mover computer; and then the secondary data mover computer receiving from the primary data mover computer a read lock on the entire file; and then the secondary data mover computer responding to the receipt of the read lock on the entire file by granting read access to the file to the first network client; and then the secondary data mover computer receiving a request from a second network client for write access to a specified byte range in the file; and then the secondary data mover computer responding to receipt of the request from the second network client for write access to the specified byte range in the file by releasing the read lock on the entire file and sending to the primary data mover computer a request for write access of the client to the specified byte range in the file; and then the secondary data mover computer receiving from the primary data mover computer an acknowledgement of a grant of write access of the client to the specified byte range in the file; and then the secondary data mover computer returning to the client the acknowledgement of the grant of write access of the client to the specified byte range in the file.