

VOL(1)                    Minix Programmer's Manual                     VOL(1)


NAME
     vol - split input on or combine output from several volumes

SYNOPSIS
     vol [-rw1] [-b blocksize] [-m multiple] [size] device

DESCRIPTION
     Vol either reads a large input stream from standard input and distributes
     it over several equal-sized volumes or combines volumes and sends them to
     standard output.  The size in  kilobytes  may  be  specified  before  the
     argument  naming  the device.  The direction of the data is automatically
     determined by checking whether the input or output of vol is  a  file  or
     pipe.   Use  the  -r  or  -w  flag  if  you want to specify the direction
     explicitly, in shell scripts for instance.

     Vol waits for each new volume to be  inserted,  typing  return  makes  it
     continue.   The  device  must  be  a block or character special.  No size
     needs to be given if the device is large and vol is  just  used  for  the
     buffering it does.

     Vol reads or writes  8192  bytes  to  block  devices,  usually  floppies.
     Character  devices  are  read  or  written using a multiple of 512 bytes.
     This multiple has an upper limit of 32767 bytes (16-bit machine),  64  kb
     (32-bit),  or  even  1  Mb  (32-bit  VM).   The  last  partial write to a
     character device is padded with zeros to the block size.  If a  character
     device is a tape device that responds to the mtio(4) status call then the
     reported tape block size will be used as the smallest unit.  If the  tape
     is a variable block length device then it is read or written like a block
     device, 8192 bytes at the time, with a minimum unit of one byte.

     All sizes may be suffixed by the letters M, k, b or  w  to  multiply  the
     number  by  mega,  kilo,  block  (512),  or word (2).  The volume size by
     default in kilobytes if there is no suffix.

OPTIONS

     -rw  Explicitly specify reading or writing.  Almost mandatory in scripts.

     -1   Just one volume, start immediately.

     -b blocksize
          Specify the device block size.

     -m multiple
          Specify the maximum read or write size of multiple blocks.   The  -b
          and  -m  options allow one to modify the block size assumptions that
          are made above.  These assumptions  are  -b  1  -m  8192  for  block
          devices  or variable length tapes, and -b 512 -m 65536 for character
          devices (32 bit machine.)  These options will not override the  tape
          block  size  found  out  with  an mtio(4) call.  The multiple may be
          larger then the default if vol can allocate the memory required.







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VOL(1)                    Minix Programmer's Manual                     VOL(1)


EXAMPLES
     To back up a tree to 1.44M floppies as a compressed tarfile:

          tar cf - . | compress | vol 1440 /dev/fd0

     To restore the tree:

          vol 1440 /dev/fd0 | uncompress | tar xfp -

     Read or write a device with 1024 byte blocks:

          vol -b 1k /dev/rsd15

     Read or write a variable block length tape using blocking  factor  20  as
     used by default by many tar(1) commands:

          vol -m 20b /dev/rst5

     Note that -m was used in the last example.  It sets the size  to  use  to
     read  or  write,  -b  sets  the  basic  block size that may be written in
     multiples.

SEE ALSO
     dd(1), tar(1), mt(1), mtio(4).


































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