as of now, ports are reused, but there is a chance that after stop/start, same brick may get different port number. This is good if a brick starts in same port as long as same glusterd instance is present. There is no need to keep this brick port info persistent, but surely for one instance of glusterd, brick should be having a port.
PATCH: http://patches.gluster.com/patch/4359 in master (mgmt/glusterd: handle port allocation so ports are reused for same brick)