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sgm_dd



SYNOPSIS

       sgm_dd [OPTION]...


DESCRIPTION

       Copy  data  to  and  from  Linux SCSI generic (sg) and raw
       devices using memory mapped IO. Similar syntax and  seman­
       tics to dd(1) but does not perform any conversions.

       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).

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

       dio=0 | 1
              permits direct IO to be selected on the  write-side
              (i.e.  "of"). Only allowed when the read-side (i.e.
              "if") is a sg device. When 1 there may be  a  "zero
              copy"  copy  (i.e.  mmap-ed IO on the read into the
              user space and direct IO from there on  the  write,
              potentially  two  DMAs and no data copying from the
              CPU). Default is 0

       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

       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

              when 1, does SYNCHRONIZE CACHE command on  "of"  at
              the  end of the transfer.  Only active when "of" is
              a sg device file name

       time=0 | 1
              when 1, times transfer and does throughput calcula­
              tion, outputting the results (to stderr) at comple­
              tion. 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 sgm_dd.  See raw(8) for more information about bind­
       ing 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  multi­
       plicative  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

       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).  With memory mapped  IO
       a  kernel  buffer reserved by sg is memory mapped (see the
       mmap(2) system call) into the user  space.  When  this  is
       done  the  second  (redundant) copy from kernel buffers to
       user space is not needed. Hence the transfer is faster and
       requires less "grunt" from the CPU.

       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 mes­
       sage is output and nothing else happens.


EXAMPLES

       See the examples given in the man page for sg_dd(8).


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 sgm_dd should not be used on tape devices.


COPYRIGHT

       Copyright © 2000-2002 Douglas Gilbert
       This  software  is  distributed  under  the GPL version 2.
       There is NO warranty; not even for MERCHANTABILITY or FIT­
       NESS FOR A PARTICULAR PURPOSE.


SEE ALSO

       The  simplest  variant of this command is called sg_dd.  A
       POSIX threads version of this command called sgp_dd is  in
       the  sg3_utils  package. The lmbench package contains lmdd
       which is also interesting.  raw(8), dd(1)

sg3_utils-1.00               May 2002                   SGM_DD(8)
  
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