126 lines
3.5 KiB
Groff
126 lines
3.5 KiB
Groff
.TH VOL 1
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.SH NAME
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vol \- split input on or combine output from several volumes
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.SH SYNOPSIS
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.B vol
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.RB [ \-rw1 ]
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.RB [ \-b
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.IR blocksize ]
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.RB [ \-m
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.IR multiple ]
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.RI [ size ]
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.I device
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.SH DESCRIPTION
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.B Vol
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either reads a large input stream from standard input and distributes it
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over several volumes or combines volumes and sends them to
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standard output. The size of the volumes is determined automatically if
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the device supports this, but may be specified before the
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argument naming the device if automated detection is not possible or if
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only part of the physical volume is used. The direction of the data is
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automatically determined by checking whether the input or output of
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.B vol
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is a file or pipe. Use the
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.B \-r
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or
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.B \-w
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flag if you want to specify the direction explicitly, in shell scripts
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for instance.
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.PP
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.B Vol
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waits for each new volume to be inserted, typing return makes it continue.
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If no size is explicitely given then the size of the device is determined
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each time before it is read or written, so it is possible to mix floppies
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of different sizes. If the size cannot be determined (probably a tape) then
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the device is assumed to be infinitely big.
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.B Vol
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can be used both for block or character devices. It will buffer the data
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and use a block size appropriate for fixed or variable block sized tapes.
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.PP
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.B Vol
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reads or writes 8192 bytes to block devices, usually floppies. Character
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devices are read or written using a multiple of 512 bytes. This multiple
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has an upper limit of 32767 bytes (16-bit machine), 64 kb (32-bit), or even
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1 Mb (32-bit VM). The last partial write to a character device is padded
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with zeros to the block size. If a character device is a tape device that
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responds to the
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.BR mtio (4)
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status call then the reported tape block size will be used as the smallest
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unit. If the tape is a variable block length device then it is read or
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written like a block device, 8192 bytes at the time, with a minimum unit
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of one byte.
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.PP
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All sizes may be suffixed by the letters
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.BR M ,
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.BR k ,
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.BR b
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or
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.BR w
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to multiply the number by mega, kilo, block (512), or word (2). The volume
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size by default in kilobytes if there is no suffix.
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.SH OPTIONS
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.TP
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.B \-rw
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Explicitly specify reading or writing. Almost mandatory in scripts.
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.TP
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.B \-1
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Just one volume, start immediately.
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.TP
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.BI \-b " blocksize"
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Specify the device block size.
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.TP
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.BI \-m " multiple"
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Specify the maximum read or write size of multiple blocks. The
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.B \-b
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and
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.B \-m
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options allow one to modify the block size assumptions that are made above.
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These assumptions are
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.B "\-b 1 \-m 8192"
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for block devices or variable length tapes, and
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.B "\-b 512 \-m 65536"
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for character devices (32 bit machine.) These options will not override the
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tape block size found out with an
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.BR mtio (4)
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call. The multiple may be larger then the default if
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.B vol
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can allocate the memory required.
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.SH EXAMPLES
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To back up a tree to floppies as a compressed tarfile:
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.PP
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.RS
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tar cf \- . | compress | vol /dev/fd0
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.RE
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.PP
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To restore a tree from 720 kb images from possibly bigger floppies:
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.PP
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.RS
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vol 720 /dev/fd0 | uncompress | tar xfp \-
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.RE
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.PP
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Read or write a device with 1024 byte blocks:
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.PP
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.RS
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vol \-b 1k /dev/rsd15
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.RE
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.PP
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Read or write a variable block length tape using blocking factor 20 as used
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by default by many
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.BR tar (1)
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commands:
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.PP
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.RS
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vol \-m 20b /dev/rst5
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.RE
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.PP
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Note that
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.B \-m
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was used in the last example. It sets the size to use to read or write,
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.B \-b
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sets the basic block size that may be written in multiples.
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.SH "SEE ALSO"
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.BR dd (1),
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.BR tar (1),
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.BR mt (1),
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.BR mtio (4).
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