path: root/sg_dd.8

.TH SG_DD "8" "March 2002" "sg3_utils-0.99" SG3_UTILS
.SH NAME
sg_dd \- copies data to and from sg and raw devices
.SH SYNOPSIS
.B sg_dd
[\fIOPTION\fR]...
.SH DESCRIPTION
.\" Add any additional description here
.PP
Copy data to and from Linux SCSI generic (sg) and raw devices.
Similar syntax and semantics to 
.B dd(1) 
but does not perform any conversions.
.TP
bpt=BLOCKS
each IO transaction will be made using this number of blocks (or less if 
near the end of count). Default is 128.
.TP
bs=BYTES
this
.B must
be the block size of the physical device. Note that this differs from
.B 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).
.TP
cdbsz=6 | 10 | 12 | 16
size of SCSI READ and/or WRITE commands issued on sg device names.
Default is 10 byte SCSI command blocks
.TP
count=BLOCKS
copy this number of blocks. Default is minimum number that sg devices
return from READ CAPACITY (if that works) or 0
.TP
dio=0 | 1
default is 0 which selects indirect IO. Value of 1 attempts direct
IO which, if not available, falls back to indirect IO and notes this
at completion. If direct IO is selected and /proc/scsi/sg/allow_dio
has the value of 0 then a warning is issued (and indirect IO is performed)
.TP
fua=0 | 1 | 2 | 3
force unit access bit. When 3, fua is set on both "if" and "of", when 2, fua
is set on "if", when 1, fua is set on "of", when 0, fua is cleared on both.
6 byte SCSI READ and WRITE commands (cdbsz=6) do not support the fua bit.
Only active for sg device file names
.TP
gen=0 | 1
the default action (when "gen=0") is to require that either "if" or "of"
is a sg or raw device name. To remove this restriction set "gen=1"
.TP
ibs=BYTES
if given must be the same as bs
.TP
if=FILE
read from FILE instead of stdin. A file name of - is taken to be stdin
.TP
obs=BYTES
if given must be the same as bs
.TP
of=FILE
write to FILE instead of stdout. A file name of - is taken to be stdout
.TP
seek=BLOCKS
skip BLOCKS bs-sized blocks at start of output
.TP
skip=BLOCKS
skip BLOCKS bs-sized blocks at start of input
.TP
sync=0 | 1
when 1, does SYNCHRONIZE CACHE command on "of" at the end of the transfer.
Only active when "of" is a sg device file name
.TP
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
.TP
--version
outputs version number information and exits
.PP
Either the input file or the output file must be a sg or raw device,
unless "gen=1".
A raw device must be bound to a block device prior to using sg_dd.
See
.B 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",
or sg_map before use.
.PP
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
.B fdisk(8)
[the "-ul" argument is useful in this respect].
.PP
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
.PP
Data usually gets to the user space in a 2 stage process: first the
SCSI adapter DMAs into kernel buffers and then the sg driver copies
this data into user memory (write operations reverse this sequence).
This is called "indirect IO" and there is a "dio" option to select
"direct IO" which will DMA directly into user memory. Due to some
issues "direct IO" is disabled in the sg driver and needs a 
configuration change to activate it. This is typically done with
"echo 1 > /proc/scsi/sg/allow_dio".
.PP
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.
.SH EXAMPLES
.PP
Looks quite similar in usage to dd:
.PP
   sg_dd if=/dev/sg0 of=t bs=512 count=1M
.PP
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:
.PP
   dd if=/dev/sda of=t bs=512 count=1000000
.PP
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:
.PP
   raw /dev/raw/raw1 /dev/hda
.br
   sg_dd if=/dev/raw/raw1 of=t bs=512 count=1M
.PP
To copy a SCSI disk partition to an IDE disk partition:
.PP
   raw /dev/raw/raw2 /dev/hda3
.br
   sg_dd if=/dev/sg0 skip=10123456 of=/dev/raw/raw2 bs=512
.PP
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.
.PP
To time a streaming read of the first 1 GB on a disk this command
could be used:
.PP
   sg_dd if=/dev/sg0 of=/dev/null bs=512 count=2m time=1
.PP
On completion this will output a line like:
"time to transfer data was 26.020794 secs, 41.26 MB/sec". The "MB/sec"
in this case is 1,000,000 bytes per second.
.SH NOTE
For sg devices this command issues READ_10 and WRITE_10 SCSI commands which
are appropriate for disks and CDROM players. Those commands are not
formatted correctly for tape devices so sg_dd should not be used on
tape devices.
.SH SIGNALS
The signal handling has been borrowed from dd: SIGINT, SIGQUIT and
SIGPIPE output the number of remaining blocks to be transferred and
the records in + out counts; then they have their default action.
SIGUSR1 causes the same information to be output yet the copy continues.
All output caused by signals is sent to stderr.
.SH AUTHORS
Written by Doug Gilbert and Peter Allworth.
.SH "REPORTING BUGS"
Report bugs to <dgilbert@interlog.com>.
.SH COPYRIGHT
Copyright \(co 2000-2002 Douglas Gilbert
.br
This software is distributed under the GPL version 2. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
.SH "SEE ALSO"
A POSIX threads version of this command called
.B sgp_dd
is in the sg3_utils package. The lmbench package contains
.B lmdd
which is also interesting.
.B raw(8), dd(1)