08-19-2015
Quote:
Originally Posted by
Don Cragun
I assume you meant bs=4 instead of bs=3, but when processing a 1.2Gb file, dd will run noticeably faster with its default block size (512 bytes) or a larger size like bs=1024000. The dd bs=n parameter specifies how many bytes dd will read at a time from its input file and how many bytes at a time it will write to its output file.
With conv=unblock, it is just the conversion buffer size (specified by cbs=n) that determines the output line length produced by the dd utility.
Although I presume the system cache and the filesystem block size will soften the blow in the sense that usually this should translate into io sizes that are equivalent to the filesystem block size or multiples thereof, depending on how smart the filesystem is...
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DD(1) FSF DD(1)
NAME
dd - convert and copy a file
SYNOPSIS
dd [OPTION]...
DESCRIPTION
Copy a file, converting and formatting according to the options.
bs=BYTES
force ibs=BYTES and obs=BYTES
cbs=BYTES
convert BYTES bytes at a time
conv=KEYWORDS
convert the file as per the comma separated keyword list
count=BLOCKS
copy only BLOCKS input blocks
ibs=BYTES
read BYTES bytes at a time
if=FILE
read from FILE instead of stdin
obs=BYTES
write BYTES bytes at a time
of=FILE
write to FILE instead of stdout
seek=BLOCKS
skip BLOCKS obs-sized blocks at start of output
skip=BLOCKS
skip BLOCKS ibs-sized blocks at start of input
--help display this help and exit
--version
output version information and exit
BLOCKS and BYTES may be followed by the following multiplicative suffixes: xM M, c 1, w 2, b 512, kB 1000, K 1024, MB 1,000,000, M
1,048,576, GB 1,000,000,000, G 1,073,741,824, and so on for T, P, E, Z, Y. Each KEYWORD may be:
ascii from EBCDIC to ASCII
ebcdic from ASCII to EBCDIC
ibm from ASCII to alternated EBCDIC
block pad newline-terminated records with spaces to cbs-size
unblock
replace trailing spaces in cbs-size records with newline
lcase change upper case to lower case
notrunc
do not truncate the output file
ucase change lower case to upper case
swab swap every pair of input bytes
noerror
continue after read errors
sync pad every input block with NULs to ibs-size; when used
with block or unblock, pad with spaces rather than NULs
AUTHOR
Written by Paul Rubin, David MacKenzie, and Stuart Kemp.
REPORTING BUGS
Report bugs to <bug-coreutils@gnu.org>.
COPYRIGHT
Copyright (C) 2002 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU-
LAR PURPOSE.
SEE ALSO
The full documentation for dd is maintained as a Texinfo manual. If the info and dd programs are properly installed at your site, the com-
mand
info dd
should give you access to the complete manual.
dd (coreutils) 4.5.3 February 2003 DD(1)