VOL(1)VOL(1)NAMEvol - split input on or combine output from several volumes
SYNOPSISvol [-rw1] [-b blocksize] [-m multiple] [size] device
DESCRIPTION
Vol either reads a large input stream from standard input and distrib‐
utes it over several volumes or combines volumes and sends them to
standard output. The size of the volumes is determined automatically
if the device supports this, but may be specified before the argument
naming the device if automated detection is not possible or if only
part of the physical volume is used. 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. If no size is explicitely given then the size of the device
is determined each time before it is read or written, so it is possible
to mix floppies of different sizes. If the size cannot be determined
(probably a tape) then the device is assumed to be infinitely big. Vol
can be used both for block or character devices. It will buffer the
data and use a block size appropriate for fixed or variable block sized
tapes.
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 char‐
acter 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.
EXAMPLES
To back up a tree to floppies as a compressed tarfile:
tar cf - . | compress | vol /dev/fd0
To restore a tree from 720 kb images from possibly bigger floppies:
vol 720 /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 mul‐
tiples.
SEE ALSOdd(1), tar(1), mt(1), mtio(4).
VOL(1)
