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Minix/CD-ROM-2.0/MINIX/MANUALS/MAN1/VOL.1

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+.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).