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 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.

OPTIONS

       -s is only available for split_output mode an leads dar_split to perform sync writes in place  of  normal
       writes.  This  has  the  drawback  to  drastically reduce performances but may be necessary under certain
       circumstances 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 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 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/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 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)