Ubuntu Manpage: sgp_dd - copy data to and from files and devices, especially SCSI devices

Provided by: sg3-utils_1.46-3ubuntu4_amd64

NAME

       sgp_dd - copy data to and from files and devices, especially SCSI devices

SYNOPSIS

       sgp_dd   [bs=BS]  [count=COUNT]  [ibs=BS]  [if=IFILE]  [iflag=FLAGS]  [obs=BS]  [of=OFILE]  [oflag=FLAGS]
       [seek=SEEK] [skip=SKIP] [--help] [--version]

       [bpt=BPT]   [coe=0|1]   [cdbsz=6|10|12|16]   [deb=VERB]   [dio=0|1]   [sync=0|1]   [thr=THR]   [time=0|1]
       [verbose=VERB] [--dry-run] [--verbose]

DESCRIPTION

       Copy  data  to  and  from  any  files.  Specialised  for "files" that are Linux SCSI generic (sg) and raw
       devices. Similar syntax and semantics to dd(1) but does not perform any conversions. Uses  POSIX  threads
       (often called "pthreads") to increase the amount of parallelism. This improves speed in some cases.

       The  first  group  in  the  synopsis above are "standard" Unix dd(1) operands. The second group are extra
       options added by this utility.  Both groups are defined below.

OPTIONS

bpt=BPT
each IO transaction will be made using BPT blocks (or less if near the end of the copy). Default
is 128 for block sizes less that 2048 bytes, otherwise the default is 32. So for bs=512 the reads
and writes will each convey 64 KiB of data by default (less if near the end of the transfer or
memory restrictions). When cd/dvd drives are accessed, the block size is typically 2048 bytes and
bpt defaults to 32 which again implies 64 KiB transfers.

bs=BS where BS must be the block size of the physical device. Note that this differs from dd(1) which
permits 'bs' to be an integral multiple of the actual device block size. Default is 512 which is
usually correct for disks but incorrect for cdroms (which normally have 2048 byte blocks).

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 (unless calculations indicate that a 4 byte block number may be exceeded, in which
case it defaults to 16 byte SCSI commands).

coe=0 | 1
set to 1 for continue on error. Only applies to errors on sg devices. Thus errors on other files
will stop sgp_dd. Default is 0 which implies stop on any error. See the 'coe' flag for more
information.

count=COUNT
copy COUNT blocks from IFILE to OFILE. Default is the minimum (of IFILE and OFILE) number of
blocks that sg devices report from SCSI READ CAPACITY commands or that block devices (or their
partitions) report. Normal files are not probed for their size. If skip=SKIP or seek=SEEK are
given and the count is deduced (i.e. not explicitly given) then that count is scaled back so that
the copy will not overrun the device. If the file name is a block device partition and COUNT is
not given then the size of the partition rather than the size of the whole device is used. If
COUNT is not given and cannot be deduced then an error message is issued and no copy takes place.

deb=VERB
outputs debug information. If VERB is 0 (default) then there is minimal debug information and as
VERB increases so does the amount of debug (max debug output when VERB is 9).

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)
For finer grain control use 'iflag=dio' or 'oflag=dio'.

ibs=BS if given must be the same as BS given to 'bs=' option.

if=IFILE
read from IFILE instead of stdin. If IFILE is '-' then stdin is read. Starts reading at the
beginning of IFILE unless SKIP is given.

iflag=FLAGS
where FLAGS is a comma separated list of one or more flags outlined below. These flags are
associated with IFILE and are ignored when IFILE is stdin.

obs=BS if given must be the same as BS given to 'bs=' option.

of=OFILE
write to OFILE instead of stdout. If OFILE is '-' then writes to stdout. If OFILE is /dev/null
then no actual writes are performed. If OFILE is '.' (period) then it is treated the same way as
/dev/null (this is a shorthand notation). If OFILE exists then it is _not_ truncated; it is
overwritten from the start of OFILE unless 'oflag=append' or SEEK is given.

oflag=FLAGS
where FLAGS is a comma separated list of one or more flags outlined below. These flags are
associated with OFILE and are ignored when OFILE is /dev/null, '.' (period), or stdout.

seek=SEEK
start writing SEEK bs-sized blocks from the start of OFILE. Default is block 0 (i.e. start of
file).

skip=SKIP
start reading SKIP bs-sized blocks from the start of IFILE. Default is block 0 (i.e. start of
file).

sync=0 | 1
when 1, does SYNCHRONIZE CACHE command on OFILE at the end of the transfer. Only active when OFILE
is a sg device file name.

thr=THR
where THR is the number or worker threads (default 4) that attempt to copy in parallel. Minimum is
1 and maximum is 1024.

time=0 | 1
when 1, the transfer is timed and throughput calculation is performed, outputting the results (to
stderr) at completion. When 0 (default) no timing is performed.

verbose=VERB
increase verbosity. Same as deb=VERB. Added for compatibility with sg_dd and sgm_dd.

-d, --dry-run
does all the command line parsing and preparation but bypasses the actual copy or read. That
preparation may include opening IFILE or OFILE to determine their lengths. This option may be
useful for testing the syntax of complex command line invocations in advance of executing them.

-h, --help
outputs usage message and exits.

-v, --verbose
when used once, this is equivalent to verbose=1. When used twice (e.g. "-vv") this is equivalent
to verbose=2, etc.

-V, --version
outputs version number information and exits.

FLAGS

Here is a list of flags and their meanings:

append causes the O_APPEND flag to be added to the open of OFILE. For normal files this will lead to data
appended to the end of any existing data. Cannot be used together with the seek=SEEK option as
they conflict. The default action of this utility is to overwrite any existing data from the
beginning of the file or, if SEEK is given, starting at block SEEK. Note that attempting to
'append' to a device file (e.g. a disk) will usually be ignored or may cause an error to be
reported.

coe continue on error. When given with 'iflag=', an error that is detected in a single SCSI command
(typically 'bpt' blocks) is noted (by an error message sent to stderr), then zeros are substituted
into the buffer for the corresponding write operation and the copy continues. Note that the sg_dd
utility is more sophisticated in such error situations when 'iflag=coe'. When given with
'oflag=', any error reported by a SCSI WRITE command is reported to stderr and the copy continues
(as if nothing went wrong).

dio request the sg device node associated with this flag does direct IO. If direct IO is 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).

direct causes the O_DIRECT flag to be added to the open of IFILE and/or OFILE. This flag requires some
memory alignment on IO. Hence user memory buffers are aligned to the page size. Has no effect on
sg, normal or raw files.

dpo set the DPO bit (disable page out) in SCSI READ and WRITE commands. Not supported for 6 byte cdb
variants of READ and WRITE. Indicates that data is unlikely to be required to stay in device (e.g.
disk) cache. May speed media copy and/or cause a media copy to have less impact on other device
users.

dsync causes the O_SYNC flag to be added to the open of IFILE and/or OFILE. The 'd' is prepended to
lower confusion with the 'sync=0|1' option which has another action (i.e. a synchronisation to
media at the end of the transfer).

excl causes the O_EXCL flag to be added to the open of IFILE and/or OFILE.

mmap can only be used in the iflag=FLAGS or the oflag=FLAGS argument list but not both. The nominated
side of the copy will use memory mapped IO based on the mmap(2) system call. The sg driver will
remap its DMA destination or source buffer into the user space when the mmap(2) system call is
used on a sg device.

fua causes the FUA (force unit access) bit to be set in SCSI READ and/or WRITE commands. This only has
effect with sg devices. The 6 byte variants of the SCSI READ and WRITE commands do not support the
FUA bit. Only active for sg device file names.

null has no affect, just a placeholder.

RETIRED OPTIONS

       Here are some retired options that are still present:

       coe=0 | 1
              continue  on  error is 0 (off) by default. When it is 1, it is equivalent to 'iflag=coe oflag=coe'
              described in the FLAGS section above.  Similar to 'conv=noerror,sync' in dd(1) utility. Default is
              0  which  implies stop on error. More advanced coe=1 processing on reads is performed by the sg_dd
              utility.

       fua=0 | 1 | 2 | 3
              force unit access bit. When 3, fua is set on both IFILE and OFILE; when 2, fua is set  on  IFILE;,
              when 1, fua is set on OFILE; when 0 (default), fua is cleared on both. See the 'fua' flag.

NOTES

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.

Raw device partition information can often be found with fdisk(8) [the "-ul" argument is useful in this
respect].

Various numeric arguments (e.g. SKIP) may include multiplicative suffixes or be given in hexadecimal. See
the "NUMERIC ARGUMENTS" section in the sg3_utils(8) man page.

The COUNT, SKIP and SEEK arguments can take 64 bit values (i.e. very big numbers). Other values are
limited to what can fit in a signed 32 bit number.

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.

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.

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.

EXAMPLES

       Looks quite similar in usage to dd:

          sgp_dd if=/dev/sg0 of=t bs=512 count=1MB

       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 correspondingly scaled. Using a raw device
       to do something similar on a ATA disk:

          raw /dev/raw/raw1 /dev/hda
          sgp_dd if=/dev/raw/raw1 of=t bs=512 count=1MB

       To copy a SCSI disk partition to an ATA 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

EXIT STATUS

       The exit status of sgp_dd is 0 when it is successful. Otherwise see the sg3_utils(8) man page. Since this
       utility  works  at  a  higher  level  than  individual commands, and there are 'coe' and 'retries' flags,
       individual SCSI command failures do not necessary cause the process to exit.

AUTHORS

       Written by Douglas Gilbert and Peter Allworth.

REPORTING BUGS

       Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT

       Copyright © 2000-2020 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.