phpman > man > sgp_dd(8)

SGP_DD(8)                                     SG3_UTILS                                    SGP_DD(8)



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 nor‐
              mally 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 par‐
              tition  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 informa‐
              tion  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 se‐
              lected 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 ac‐
              tive 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  paral‐
              lel. 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 over‐
              write  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 re‐
              quires 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 process‐
              ing 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  in‐
       formation  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 use‐
       ful 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 val‐
       ues 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 re‐
       verse  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  dis‐
       abled 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 er‐
       rors 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 MER‐
       CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO
       A simpler, non-threaded version of this utility but with more advanced  "continue  on  error"
       logic  is  called  sg_dd and is also found in the sg3_utils package. The lmbench package con‐
       tains lmdd which is also interesting.  raw(8), dd(1)



sg3_utils-1.45                              February 2020                                  SGP_DD(8)