Provided by: sg-utils_1.02-1_i386
copies data to and from sg and raw devices
Copy data to and from Linux SCSI generic (sg), raw devices or normal
files. Similar syntax and semantics to dd(1) but does not perform any
conversions. Uses POSIX threads to increase the amount of parallelism.
This improves speed in some cases.
each IO transaction will be made using this number of blocks (or
less if near the end of count). Default is 128.
this must be the block size of the physical device. Note that
this differs from dd(1) which permits "bs" to be an integral
multiple. Default is 512 which is usually correct for disks but
incorrect for cdroms (which normally have 2048 byte blocks).
coe=0 | 1
continue on error is 0 (off) by default. When it is 1 read
errors are stepped over (with a block (or blocks) of zeroes
copy this number of blocks. Default is minimum number that sg
devices return from READ CAPACITY (if that works) or 0
outputs debug information. If NUM is 0 (default) then none and
as NUM increases so does the amount of debug (max debug output
when NUM is 9)
if given must be the same as bs
read from FILE instead of stdin. A file name of - is taken to be
if given must be the same as bs
write to FILE instead of stdout. A file name of - is taken to be
skip BLOCKS bs-sized blocks at start of output
skip BLOCKS bs-sized blocks at start of input
this is the number or worker threads (default 4) that attempt to
copy in parallel. Minimum is 0 and maximum is 16
time=0 | 1
when 1, times transfer and does throughput calculation,
outputting the results (to stderr) at completion. When 0
(default) doesn’t perform timing
outputs version number information and exits
A raw device must be bound to a block device prior to using sgp_dd.
See raw(8) for more information about binding raw devices. To be safe,
the sg device mapping to SCSI block devices should be checked with "cat
/proc/scsi/scsi" before use.
The count is only deduced for sg devices (minimum > 0 if both input and
output are sg devices) otherwise it defaults to 0. This is for safety!
Raw device partition information can often be found with fdisk(8) [the
"-ul" argument is useful in this respect].
BYTES and BLOCKS may be followed by the following multiplicative
suffixes: c C *1; b B *512; k *1,024; K *1,000; m *1,048,576; M
*1,000,000; g *1,073,741,824; and G *1,000,000,000
All informative, warning and error output is sent to stderr so that
dd´s output file can be stdout and remain unpolluted. If no options are
given, then the usage message is output and nothing else happens.
Why use sgp_dd? Because in some cases it is twice as fast as dd (mainly
with sg devices, raw devices give some improvement). Another reason is
that big copies fill the block device caches which has a negative
impact on other machine activity.
Looks quite similar in usage to dd:
sgp_dd if=/dev/sg0 of=t bs=512 count=1M
This will copy 1 million 512 byte blocks from the device associated
with /dev/sg0 (which should have 512 byte blocks) to a file called t.
Assuming /dev/sda and /dev/sg0 are the same device then the above is
dd if=/dev/sda of=t bs=512 count=1000000
although dd´s speed may improve if bs was larger and count was suitably
reduced. Using a raw device to do something similar on a IDE disk:
raw /dev/raw/raw1 /dev/hda
sgp_dd if=/dev/raw/raw1 of=t bs=512 count=1M
To copy a SCSI disk partition to an IDE disk partition:
raw /dev/raw/raw2 /dev/hda3
sgp_dd if=/dev/sg0 skip=10123456 of=/dev/raw/raw2 bs=512
This assumes a valid partition is found on the SCSI disk at the given
skip block address (past the 5 GB point of that disk) and that the
partition goes to the end of the SCSI disk. An explicit count is
probably a safer option.
To do a fast copy from one SCSI disk to another one with similar
geometry (stepping over errors on the source disk):
sgp_dd if=/dev/sg0 of=/dev/sg1 bs=512 coe=1
Written by Doug Gilbert and Peter Allworth.
Report bugs to <email@example.com>.
Copyright © 2000 Douglas Gilbert
This software is distributed under the GPL version 2. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
A simpler, non-threaded version of this command called sg_dd is in the
sg_utils package. The lmbench package contains lmdd which is also
interesting. raw(8), dd(1)