bsd man page for ddd

DDD(1L) 																   DDD(1L)

NAME
       ddd - double-speed data dumper

SYNOPSIS
       ddd [option=value] ...

DESCRIPTION
       Ddd  works  almost  the	same  way  as dd(1), but it has a much better throughput, especially when used with slow i/o-devices, such as tape
       drives.	The improvement is achieved mainly by dividing the copying process into two processes, one of which  reads  while  the	other  one
       writes  and  vice  versa.  Also all code conversion capabilities are omitted.  There is no additional overhead copying data between various
       conversion buffers.

       Ddd was inspired by the vast difference in speed between BSD4.2 and BSD4.3 dumps - in BSD4.3 dump(8) uses alternating processes to write to
       raw  magnetic tape, thus keeping the tape continuously in motion.  I wanted to get the same improvement to remote dumps, so this filter was
       needed.	Directing all physical I/O through ddd usually increases the throughput of any pipeline of unix commands (if you have enough  MIPS
       and RAM to handle two extra processes).

OPTIONS
       Ddd  uses  options  if,	of,  ibs and obs exactly as dd(1).  Option bs can also be used to specify ibs and obs at once.	One option differs
       slightly in meaning: cbs can be used to specify the size of the internal buffer.  Input and output processes  will  swap  duties  when  cbs
       bytes  have  been transferred.  Default values for all sizes are 512 bytes.  As with dd(1), letters k (kilobyte), b (block) or w (word) can
       be appended to size values.  Other options are not provided.

HINTS
       For best performance, block sizes should be rather large.  For magnetic tape, I use obs=100b and cbs=500b or so.  Large block sizes (~100b)
       are  also  effective  for  network connections.	However, cbs should be small enough for all the data to fit in core, since page faults add
       overhead.

AUTHOR
       Tapani Lindgren <nispa@cs.hut.fi>
       Laboratory of Information Processing Science
       Helsinki University of Technology
       Finland

SEE ALSO
       dd(1), tar(1), dump(8)

BUGS
       Should you find one, let me know!

WARNING
       (Applies to U.S. residents & citizens only)
       Do not use this program!  Get rid of it as soon as you can!  It will probably corrupt all your data, break down	your  computer	and  cause
       severe  injury to the operators.  Even reading the source code may give you a headache.	I warned you!  I will take no responsibility what-
       soever!

																	   DDD(1L)