125 lines
3.5 KiB
Groff
125 lines
3.5 KiB
Groff
.TH VOL 1
|
|
.SH NAME
|
|
vol \- split input on or combine output from several volumes
|
|
.SH SYNOPSIS
|
|
.B vol
|
|
.RB [ \-rw1 ]
|
|
.RB [ \-b
|
|
.IR blocksize ]
|
|
.RB [ \-m
|
|
.IR multiple ]
|
|
.RI [ size ]
|
|
.I device
|
|
.SH DESCRIPTION
|
|
.B Vol
|
|
either reads a large input stream from standard input and distributes 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
|
|
.B vol
|
|
is a file or pipe. Use the
|
|
.B \-r
|
|
or
|
|
.B \-w
|
|
flag if you want to specify the direction explicitly, in shell scripts
|
|
for instance.
|
|
.PP
|
|
.B 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.
|
|
.B 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.
|
|
.PP
|
|
.B 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
|
|
.BR 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.
|
|
.PP
|
|
All sizes may be suffixed by the letters
|
|
.BR M ,
|
|
.BR k ,
|
|
.BR b
|
|
or
|
|
.BR 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.
|
|
.SH OPTIONS
|
|
.TP
|
|
.B \-rw
|
|
Explicitly specify reading or writing. Almost mandatory in scripts.
|
|
.TP
|
|
.B \-1
|
|
Just one volume, start immediately.
|
|
.TP
|
|
.BI \-b " blocksize"
|
|
Specify the device block size.
|
|
.TP
|
|
.BI \-m " multiple"
|
|
Specify the maximum read or write size of multiple blocks. The
|
|
.B \-b
|
|
and
|
|
.B \-m
|
|
options allow one to modify the block size assumptions that are made above.
|
|
These assumptions are
|
|
.B "\-b 1 \-m 8192"
|
|
for block devices or variable length tapes, and
|
|
.B "\-b 512 \-m 65536"
|
|
for character devices (32 bit machine.) These options will not override the
|
|
tape block size found out with an
|
|
.BR mtio (4)
|
|
call. The multiple may be larger then the default if
|
|
.B vol
|
|
can allocate the memory required.
|
|
.SH EXAMPLES
|
|
To back up a tree to floppies as a compressed tarfile:
|
|
.PP
|
|
.RS
|
|
tar cf \- . | compress | vol /dev/fd0
|
|
.RE
|
|
.PP
|
|
To restore a tree from 720 kb images from possibly bigger floppies:
|
|
.PP
|
|
.RS
|
|
vol 720 /dev/fd0 | uncompress | tar xfp \-
|
|
.RE
|
|
.PP
|
|
Read or write a device with 1024 byte blocks:
|
|
.PP
|
|
.RS
|
|
vol \-b 1k /dev/rsd15
|
|
.RE
|
|
.PP
|
|
Read or write a variable block length tape using blocking factor 20 as used
|
|
by default by many
|
|
.BR tar (1)
|
|
commands:
|
|
.PP
|
|
.RS
|
|
vol \-m 20b /dev/rst5
|
|
.RE
|
|
.PP
|
|
Note that
|
|
.B \-m
|
|
was used in the last example. It sets the size to use to read or write,
|
|
.B \-b
|
|
sets the basic block size that may be written in multiples.
|
|
.SH "SEE ALSO"
|
|
.BR dd (1),
|
|
.BR tar (1),
|
|
.BR mt (1),
|
|
.BR mtio (4).
|