[root@centos /]$ time dd if=/dev/zero of=/data/test bs=8k count=1000000
1000000+0 records in
1000000+0 records out
8192000000 bytes (8.2 GB) copied, 24.5315 s, 334 MB/s
real 0m24.534s
user 0m0.208s
sys 0m12.931s
[root@centos /]$ time dd if=/data/test of=/dev/null bs=8k
1000000+0 records in
1000000+0 records out
8192000000 bytes (8.2 GB) copied, 18.6046 s, 440 MB/s
real 0m18.670s
user 0m0.017s
sys 0m13.771s
上面简单测试了下，/data上面硬盘的读写速度。
[root@centos /]$ dd –help
Usage: dd [OPERAND]…
or: dd OPTION
Copy a file, converting and formatting according to the operands.
参数选项
bs=BYTES read and write BYTES bytes at a time (also see ibs=,obs=)
cbs=BYTES convert BYTES bytes at a time
conv=CONVS convert the file as per the comma separated symbol list
count=BLOCKS copy only BLOCKS input blocks
ibs=BYTES read BYTES bytes at a time (default: 512)
if=FILE read from FILE instead of stdin
iflag=FLAGS read as per the comma separated symbol list
obs=BYTES write BYTES bytes at a time (default: 512)
of=FILE write to FILE instead of stdout
oflag=FLAGS write as per the comma separated symbol list
seek=BLOCKS skip BLOCKS obs-sized blocks at start of output
skip=BLOCKS skip BLOCKS ibs-sized blocks at start of input
status=WHICH WHICH info to suppress outputting to stderr;
‘noxfer’ suppresses transfer stats, ‘none’ suppresses all
BLOCKS and BYTES may be followed by the following multiplicative suffixes:
c =1, w =2, b =512, kB =1000, K =1024, MB =1000*1000, M =1024*1024, xM =M
GB =1000*1000*1000, G =1024*1024*1024, and so on for T, P, E, Z, Y.
Each CONV symbol may be:
ascii from EBCDIC to ASCII
ebcdic from ASCII to EBCDIC
ibm from ASCII to alternate 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
nocreat do not create the output file
excl fail if the output file already exists
notrunc do not truncate the output file
ucase change lower case to upper case
sparse try to seek rather than write the output for NUL input blocks
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
fdatasync physically write output file data before finishing
fsync likewise, but also write metadata
Each FLAG symbol may be:
append append mode (makes sense only for output; conv=notrunc suggested)
direct use direct I/O for data
directory fail unless a directory
dsync use synchronized I/O for data
sync likewise, but also for metadata
fullblock accumulate full blocks of input (iflag only)
nonblock use non-blocking I/O
noatime do not update access time
noctty do not assign controlling terminal from file
nofollow do not follow symlinks
Sending a USR1 signal to a running `dd’ process makes it
print I/O statistics to standard error and then resume copying.
$ dd if=/dev/zero of=/dev/null& pid=$!
$ kill -USR1 $pid; sleep 1; kill $pid
18335302+0 records in
18335302+0 records out
9387674624 bytes (9.4 GB) copied, 34.6279 seconds, 271 MB/s