If the diskette contains a mounted file system, you must unmount the file system before running tar. You can unmount the file system using the umount command, or you can unmount the file system and format the diskette using the fdformat -U command.
Copying files to a formatted diskette using the -c option of tar destroys any files already on the diskette.
Reformatting a diskette destroys any files or archives that were already on the diskette.