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DAR_SPLIT(1)           DragonFly General Commands Manual          DAR_SPLIT(1)


NAME

       dar_split - dar helper to split an archive over several tapes


SYNOPSIS

       dar_split { split_input | split_output } <filename>

       dar_split -v

       dar_split -h


DESCRIPTION

       dar_split is to be used with dar to read or write a large archive from
       or to several tapes.


OPTIONS

       dar_split has two modes of operation: split_input and split_output

       split_input         in this mode dar_split copies <filename> to its
                           standard output. <filename> may be a special device
                           like /dev/tape or any other inode that has the
                           ability to access removeable volumes. When
                           dar_split reaches the end of <filename> it suspends
                           and waits for the user to press the return key in
                           order to continue. In the meanwhile the user can
                           rewind and change the tape. When dar_split is
                           awaken again, it reopens <filename> and sends its
                           content to its standard output as if it was the
                           continuation of what was read so far before
                           reaching the end of file.

       split_output        in this mode dar_split copies its standard input to
                           <filename>. However if <filename> is full,
                           dar_split suspends and waits for the user to press
                           the return key in order to continue. In the
                           meanwhile, the user can rewind and change the tape.
                           When dar_split is awaken again, it reopens
                           <filename> and continues to copy to <filename> what
                           was not yet written previously.


EXAMPLES OF USE

       creating an archive over several tapes

              dar -c - ...possibily other dar options... | dar_split
              split_output /dev/tape

       Here dar generates the archive to its standard output which is read by
       dar_split and copied to /dev/tape. When the tape reaches its send,
       dar_split asks for the user to hit return to continue.

       reading an archive splitted over several tapes

              dar_split split_input /dev/tape | dar -t - --sequential-read
              ...possibily other dar options...

       Here dar_split reads /dev/tape and sends its content to dar which
       *must* be used in --senquential-read mode in order to read an archive
       from its standard input without the help of dar_slave. When the tape
       reaches its end, dar_split asks for the user to hit return to continue.

       Note that dar_split can also be used with tar for the same purpose as
       with dar:

              tar -cz ... | dar_split split_output /dev/tape

       without -f option nor TAPE environment variable, tar sends the tar
       archive to stdout, which get fet to dar_split for slicing

              dar_split split_input /dev/tape | tar -tz

       without -f option nor TAPE environement variable, tar read the tar
       archive from stdin, however you must specify the correct option
       corresponding to the compression used at archive creation time.

       The advantage here is to be able to save a huge dar or tar archive on
       several tapes that could be either partially filled or having different
       sizes, without having to calculate in advance the size of slices to
       specify. The drawback is that this implies sequential reading for dar
       (for tar also, but tar cannot do else).

With or without filesystem
       You can use dar_split with floppies, zip/jazz disks or usb key too, but
       it has many disadvantages compared to the normal way of using this
       media: doing that way avoids you relying on a filesystem, thus you
       cannot have direct access to file contents, which dar knows how to take
       advantage of, and you are instead stuck with sequential read access
       which is long as it requires reading the whole archive (same way as tar
       does).

       When instead using dar alone in normal mode (non sequential reading
       mode using filenames instead of standard input/output), you have the
       opportunity to create redundancy data beside dar slices thanks to par2,
       which is not possible without a filesystem. At restorationt time,
       thanks to dar archive's catalog, dar can directly seek to the file's
       data you want to restore, which is very quick compared to
       reading/unciphering/uncompressing the whole archive...

       Note that copying tape contents generated by dar_split to different
       files which name would correspond to dar slices, does not make a valid
       multi-sliced archive because the slice header is missing in slices
       (except in the first). You can however concatenate all the pieces of
       data generated by dar_split and have a valid single sliced dar archive
       that you can use in direct access mode. However attention must be paied
       not to add any extra data after data generated by dar through dar_split
       (in particular if the last tape was not full), in that case you are
       stuck with --sequential-read mode.


EXIT CODES

       dar_split exists with the following codes:

       0         upon normal execution

       1         syntax error on command-line

       2         could not open source or destination files


SIGNALS

       Any signal sent to dar_split except SIG_PIPE will abort the program
       immediately


SEE ALSO

       dar(1), dar_xform(1), dar_manager(1), dar_slave(1), dar_cp(1)


KNOWN BUGS

       http://sourceforge.net/p/dar/bugs/


AUTHOR

       http://dar.linux.free.fr/
       Denis Corbin
       France
       Europe

3rd Berkeley Distribution      April 12th, 2015                   DAR_SPLIT(1)

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