Go to the previous, next section.
(This message will disappear, once this node revised.)
Often you might want to write a large archive, one larger than will fit
on the actual tape you are using. In such a case, you can run multiple
tar commands, but this can be inconvenient, particularly if you
are using options like `--exclude=pattern' or dumping entire filesystems.
Therefore, tar supports multiple tapes automatically.
Use `--multi-volume' (`-M') on the command line, and then tar will,
when it reaches the end of the tape, prompt for another tape, and
continue the archive. Each tape will have an independent archive, and
can be read without needing the other. (As an exception to this, the
file that tar was archiving when it ran out of tape will usually
be split between the two archives; in this case you need to extract from
the first archive, using `--multi-volume' (`-M'), and then put in the
second tape when prompted, so tar can restore both halves of the
file.)
When prompting for a new tape, tar accepts any of the following
responses:
tar to explain possible responses
tar to exit immediately.
tar to write the next volume on the file file name.
tar to run a subshell.
tar to begin writing the next volume.
(You should only type `y' after you have changed the tape;
otherwise tar will write over the volume it just finished.)
If you want more elaborate behavior than this, give tar the
`--info-script=script-name' (`-F script-name') option. The file script-name is expected
to be a program (or shell script) to be run instead of the normal
prompting procedure. When the program finishes, tar will
immediately begin writing the next volume. The behavior of the
`n' response to the normal tape-change prompt is not available
if you use `--info-script=script-name' (`-F script-name').
The method tar uses to detect end of tape is not perfect, and
fails on some operating systems or on some devices. You can use the
`--tape-length=1024-size' (`-L 1024-size') option if tar can't detect the end of the
tape itself. The size argument should be the size of the tape.
The volume number used by tar in its tape-change prompt
can be changed; if you give the `--volno-file=file-of-number' option, then
file-of-number should contain a decimal number. That number
will be used as the volume number of the first volume written.
When tar is finished, it will rewrite the file with the
now-current volume number. (This does not change the volume number
written on a tape label (
FIXME: pxref Special Options for Archiving; it only affects the number used in the prompt.)
If you want tar to cycle through a series of tape drives, then
you can use the `n' response to the tape-change prompt. This is
error prone, however, and doesn't work at all with `--info-script=script-name' (`-F script-name').
Therefore, if you give tar multiple `--file=archive-name' (`-f archive-name') options, then
the specified files will be used, in sequence, as the successive volumes
of the archive. Only when the first one in the sequence needs to be
used again will tar prompt for a tape change (or run the info
script).
Multi-volume archives
With `--multi-volume' (`-M'), tar will not abort when it cannot
read or write any more data. Instead, it will ask you to prepare a new
volume. If the archive is on a magnetic tape, you should change tapes
now; if the archive is on a floppy disk, you should change disks, etc.
Each volume of a multi-volume archive is an independent tar
archive, complete in itself. For example, you can list or extract any
volume alone; just don't specify `--multi-volume' (`-M'). However, if one
file in the archive is split across volumes, the only way to extract
it successfully is with a multi-volume extract command `--extract
--multi-volume' (`-xM') starting on or before the volume where
the file begins.
Go to the previous, next section.