buffer man page on Mandriva

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BUFFER(1)							     BUFFER(1)

NAME
       buffer - very fast reblocking program

SYNTAX
       buffer  [-S  size]  [-b blocks] [-s size] [-m size] [-p percentage] [-u
       microseconds] [-B] [-t] [-Z] [-i filename] [-o filename]

OPTIONS
       -i filename
	    Use the given file as the input file.  The default is stdin.

       -o filename
	    Use the given file as the output file.  The default is stdout.

       -S size
	    After every chunk of this size has been  written,  print  out  how
	    much has been written so far. Also prints the total througput.  By
	    default this is not set.

       -s size
	    Size in bytes of each block.  The  default	blocksize  is  10k  to
	    match the normal output of the tar(1) program.

       -z size
	    Combines the -S and -s flags.

       -b blocks
	    Number  of	blocks	to  allocate to shared memory circular buffer.
	    Defaults to the number required  to	 fill  up  the	shared	memory
	    requested.

       -m size
	    Maximum size of the shared memory chunk to allocate for the circu‐
	    lar queue. Defaults to one megabyte.

       -p percentage
	    Only start a write when the given percentage of the internal queue
	    is	full.	A  percentage around 75 often proves best. Defaults to
	    zero.

       -u microseconds
	    After every write pause for this many microseconds.	  Defaults  to
	    zero.  (Suprisingly a small sleep, 100 usecs, after each write can
	    greatly enhance throughput on some drives.)

       -B   Force each block written to be padded out to the blocksize.	  This
	    is	needed	by  some  tape	and  cartridge	drives.	  Defaults  to
	    unpadded.  This only affects the last block written.

       -t   On exiting print to stderr a brief message showing the total  num‐
	    ber of bytes written.

       -Z   If	reading/writing	 directly  to  a character device (like a tape
	    drive) then after each gigabyte perform an lseek to the  start  of
	    the	 file.	 Use this flag with extreme care.  It can only be used
	    on devices where an lseek does not rewind the tape but does	 reset
	    the kernels position flags.	 It is used to allow more than 2 giga‐
	    bytes to be written.

       Sizes are a number with an optional trailing character.	 A 'b'	multi‐
       plies the size by 512, a 'k' by 1024 and an 'm' by a meg.

DESCRIPTION
       Buffer  reads from standard input reblocking to the given blocksize and
       writes each block to standard output.

       Internally buffer is a pair of processes communicating via a large cir‐
       cular  queue  held  in  shared  memory.	The reader process only has to
       block when the queue is full and the writer process when the  queue  is
       empty.  Buffer is designed to try and keep the writer side continuously
       busy so that it can stream when writing to tape drives.	When  used  to
       write  tapes with an intervening network buffer can result in a consid‐
       erable increase in throughput.

       The default settings for buffer are normally good enough.  If you are a
       heavy  tape user then it is worth your while trying out various differ‐
       ent combinations of options.  In particular running a  buffer  at  both
       ends  of	 the pipe can provide a substantial increase (see last example
       below).

EXAMPLES
       $ buffer < /etc/termcap > /dev/rst8

       $ tar cf - . | rsh somehost 'buffer > /dev/rst8'

       $ dump fu - | rsh somehost 'buffer -s 16k > /dev/nrst8'
       $ tar cf - . | buffer |
	  rsh somehost 'buffer -S 500K -p 75 > /dev/rst0'

BUGS
       Internally, for printing purposes, buffer counts in terms of the number
       of kilobytes output.  If the blocksize you use is not a whole number of
       kilobytes then the numbers printed will be inaccurate.

THANKS
       Thanks to Kevin Twidle <kpt@doc.ic.ac.uk> for a lot  of	early  sugges‐
       tions  and  patches  to make it work with non-tar/dump tapes to exabyte
       drives.

       Thanks	to   Andi   Karrer   <karrer@bernina.ethz.ch>,	 Rumi	 Zahir
       <rumi@iis.ethz.ch>  and Christoph Wicki <wicki@iis.ethz.ch> for patches
       to make buffer work when trying to write single tape files  of  greater
       than 2 gigabytes.

COPYRIGHT
       Copyright (C) 1990, 1991 by Lee McLoughlin.

SEE ALSO
       dd(1), tar(1), rsh(1)

				  14 May 1990			     BUFFER(1)
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