In general, SAP recommends that you do not dump a file or disk. If the disk or computer containing that file fails, there may be no way to recover the data.
On UNIX and PC systems, the entire master database dump must fit into a single volume. On these systems, dumping to a file or disk is your only option if the master database is too large to fit on a single tape volume, unless you have a second SAP ASE that can issue sp_volchanged requests.
You can copy dumps to a file or disk to tape for offline storage, but these tapes must be copied back to an online file before they can be read by SAP ASE. Backup Server cannot directly read a dump that is made to a disk file and then copied to tape.