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dar_split(1)                                                      dar_split(1)




NAME

       dar_split - dar helper to split an archive over several tapes


SYNOPSIS

       dar_split { split_input | [-s] 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.



COMMANDS

       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  reach-
                           ing 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  mean-
                           while,  the  user  can  rewind and change the tape.
                           When dar_split is awaken again, it  reopens  <file-
                           name>  and continues to copy to <filename> what was
                           not yet written previously.



OPTIONS

       -s is only available for split_output mode an leads dar_split  to  per-
       form  sync  writes  in place of normal writes. This has the drawback to
       drastically reduce performances but may be necessary under certain cir-
       cumstances  where  the operating system cache reports a write operation
       as successful while the cache underlying medium is already full.



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 ar-
       chive 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  ar-
       chive  from  stdin,  however you must specify the correct option corre-
       sponding 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 can-
       not  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 restoration 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/uncipher-
       ing/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 can
       only read the archive 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      August 18th, 2018                  dar_split(1)

dar 2.6.1 - Generated Sat Jan 26 15:22:01 CST 2019
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