I got this point from a book,it saysBecause the tape device is a disposable I/O device,so we can't use  commands like 'cp' to copy.And the author recommended to use 'tar':tar -cvf /dev/st0 /homeI know 'cp' will read and write contents to somewhere repeatedly,but I think use 'cp' to copy things to the tape device can also succeed.But I don't have such device and can't validate my assumption.So,your opinions?
Why can't the tape device such as '/dev/st0' use commands like 'cp' to copy contents to it?
tar;tape
You use cp to copy a file to another file, not to a device. You can't send a file to the printer with cp file /dev/lp0 either.You may be able to use cat file > /dev/st0 to write the file to tape, but then you would have no way to know what the name of the file was, nor its permissions or other metadata. tar prefixes the file data with a header containing that information so that it can be reconstructed when reading it back.BTW I don't know what your book means with disposable I/O device; it's a character device (which ironically means that you can only write aligned blocks to it). This also means that the cat command above may fail at the end if the file size is not an exact multiple of the required block size.So just use tar :-)