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mbuffer(1)			console	utility			    mbuffer(1)

       mbuffer - measuring buffer

       mbuffer [options]

       mbuffer	buffers	I/O operations and displays the	throughput rate. It is
       multi-threaded, supports	network	connections, and offers	 more  options
       than the	standard buffer.

       -i <filename>
	      Use filename as input instead of the standard input (needs to be
	      given for	multi volume support). If filename is -, input is read
	      from standard input.

       -I <port>
	      Use network port port as input instead of	the standard input. If
	      given a hostname and a port in the form hostname:port, the first
	      interface	with the IP of hostname	will be	used.

       -o <filename>
	      Use  filename as output instead of the standard output (needs to
	      be given for multi volume	support, will enable use  of  sendfile
	      if  available).  If filename is -, output	is written to standard
	      output. The option -o can	be passed multiple  times  to  specify
	      multiple outputs.

       -O <hostname:port>
	      Write  output  to	 hostname:port	instead	of the standard	output
	      (will enable use of sendfile if available). This option  can  be
	      used multiple times to send data to multiple machines.

       -b <num>
	      Use num blocks for buffer	(default 256).

       -s <size>
	      Use  blocks  of  size bytes for buffer (default pagesize of sys-

       -m <size>
	      Use a total of size bytes	for buffer (default 2MB) - size	can be
	      set  with	a trailing character (b	and B for Byte,	k for kByte, M
	      for MByte, G for Gigabyte, and with % for	a percentage of	 total
	      physical memory).

       -L     Lock  buffer  in memory -	this option is not available for file-
	      based buffers and	requires mbuffer to be set-UID root (use  with

       -n <num>
	      num volumes in input device (requires use	of option -i for input
	      device specification) [currently multi volume support is EXPERI-

       -t     use a memory-mapped temporary file as buffer (use	with huge buf-

       -T <file>
	      as -t but	use file instead

       -d     use block-size of	device for output (needed  for	some  devices,
	      slows output down)

       -D <size>
	      assume  an  output volume	of size	bytes (default infinite) after
	      which a volume change will be initiated. Small values are	useful
	      for  the timely testing of multi-volume runs; accurate values if
	      your device doesn't properly signal end of media.	 Size  can  be
	      set  with	a trailing character (b	and B for Byte,	k for kByte, M
	      for MByte, or G for Gigabyte)

       -P <num>
	      start writing after the buffer has been filled to	num%  (default
	      0	- start	at once)

       -p <num>
	      start  reading  after the	buffer has dropped below fill-ratio of
	      num% (default 100	- start	at once)

       -l <file>
	      log messages to file instead of standard error output

       -u <num>
	      pause num	microseconds after each	write -	might increase perfor-
	      mance on some drives with	very low performance (<	1 MB/sec)

       -r <rate>
	      Set  the maximum read rate to <rate>. <rate> can be given	in ei-
	      ther Bytes, kBytes, MBytes, or GBytes per	second.	To do so,  use
	      an appropriate suffix (i.e. k,M,G). This option is useful	if you
	      have a tape that is capable of transferring data faster than the
	      host  can	 handle	 it.  In  this case you	can use	this option to
	      limit the	transfer rate and keep the tape	running. Be aware that
	      this is both good	for your tape drive, and enhances overall per-
	      formance,	by avoiding tape screwing.

       -R <rate>
	      Same as above only  for  setting	the  transfer  limit  for  the

       -A <cmd>
	      the device used is an autoloader which uses cmd to load the next

       -a <time>
	      the device used is an autoloader which  takes  time  seconds  to
	      load a new tape

       -f     overwrite	output file if it exists already

       -c     write  with  synchronous	data  integrity	 support - This	option
	      forces all writes	to complete before  continuing.	 This  enables
	      errors  to be reported earlier and more precisely, but might de-
	      crease performance. Especially systems with high level  of  data
	      integrity	 support  suffer  a huge performance hit. Others might
	      seem to be unaffected, but just neglect support  for  full  syn-
	      chronous data integrity.

       -v <num>
	      set  verbose  level to num. Valid	values are 0..6	(0 = none, 1 =
	      errors, 2	= warnings, 4 =	information messages,  5  =  debugging
	      messages,	6 = I/O	debugging). Higher values include lower	values

       -q     quiet - do not display the status	on the standard	 error	output
	      --direct	Use  O_DIRECT to open file descriptors.	This option is
	      not available on all systems. It tells the OS to bypass the page
	      cache  to	 improve  performance when reading and writing.	On So-
	      laris this is an auto-magic option that is enabled if it is sup-
	      ported  for  the	relevant file. Be aware	that this option might
	      lead to  read/write  failures,  if  the  buffer  isn't  properly
	      aligned  for direct I/O. Additionally, open might	fail with EIN-
	      VAL (i.e.	invalid	argument) if the named file does  not  support

       -6     Force IPv6 mode for the following	network	I/O options on command
	      line.  -4	Force IPv4 mode	for the	following network I/O  options
	      on command line.	-0 Choose IPv4/IPv6 mode on demand.

       -h, --help
	      Output help information and exit.

       -H, --md5
	      Generate a MD5 hash of transferred data.

       -V, --version
	      Output version information and exit.

       If  TMPDIR  is set, mbuffer allocates storage for file-based buffers in
       this directory. If TMPDIR is unset, /var/tmp will be used.


       To run this program with	the default options just type:


       Using mbuffer to	do a backup with tar to	the default tape  device.  Op-
       tions  for this example:	memory-mapped temporary	file with a size of 10
       Megabytes, start	after 80% of the buffer	have been filled.

       tar cf -	mydirectory | gzip | mbuffer -t	-m 10M -P 80 -f	-o $TAPE

       Using mbuffer with 3 tapes for input and	extracting the contents	in the
       current work directory:

       mbuffer -n 3 -i $TAPE | gzip -dc	| tar xf -

       Using mbuffer to	write to multiple tape volumes:

       tar cf -	/usr | mbuffer -f -o $TAPE

       Write to	multiple tapes and erase every tape before writing:

       tar cf -	/usr | mbuffer -A "echo	next tape; read	a < /dev/tty; mt erase
       $TAPE" -f -o $TAPE

       Making a	backup via network:

       tape server: mbuffer -I 8000 -f -o $TAPE

       backup client: tar zcf -	/home |	mbuffer	-O tapeserver:8000

       Distributing a directory	tree to	multiple machines:

       master: tar cf -	/tree_to_clone | mbuffer -O clone0:8000	-O clone1:8000

       clones: mbuffer -I master:8000 |	tar xf -

       mbuffer return 0	upon success. Any kind of failure will	yield  a  non-
       zero exit code.

       Thomas Maier-Komor <>

       If  you	like this software, and	use it for production purposes in your
       company,	please consider	making a donation to support this  work.   You
       can   donate  directly  via  PayPal  to	the  author's  e-mail  address


       This software is	published under	GNU General  Public  License  V3.  See
       file LICENSE for	details.


Thomas Maier-Komor		   20110317			    mbuffer(1)


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