copies data to and from sg and raw devices

sgp_dd [OPTION]...

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.

bpt=BLOCKS

each IO transaction will be made using this number of blocks (or less if near the end of count). Default is 128.

bs=BYTES

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 being output)

count=BLOCKS

copy this number of blocks. Default is minimum number that sg devices return from READ CAPACITY (if that works) or 0

deb=NUM

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)

ibs=BYTES

if given must be the same as bs

if=FILE

read from FILE instead of stdin. A file name of - is taken to be stdin

obs=BYTES

if given must be the same as bs

of=FILE

write to FILE instead of stdout. A file name of - is taken to be stdout

seek=BLOCKS

skip BLOCKS bs-sized blocks at start of output

skip=BLOCKS

skip BLOCKS bs-sized blocks at start of input

thr=NUM

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

--version

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 equivalent to:

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 <dgilbert@interlog.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 PURPOSE.

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)