NAME

       sg_seek - send SCSI SEEK, PRE-FETCH(10) or PRE-FETCH(16) command

SYNOPSIS

       sg_seek [--10] [--count=NC] [--grpnum=GN] [--help] [--immed] [--lba=LBA] [--num-blocks=NUM] [--pre-fetch]
       [--readonly] [--skip=SB] [--time] [--verbose] [--version] [--wrap-offset=WO] DEVICE

DESCRIPTION

       Sends a SCSI SEEK(10), PRE-FETCH(10) or PRE-FETCH(16) command to the DEVICE. The SEEK  command  has  been
       obsolete  since  SBC-2  (2005)  but still is supported on some hard disks and even some SSDs (solid state
       disks). The PRE-FETCH command can be viewed as SEEK's  modern  replacement.   Instead  of  talking  about
       moving  the disk heads to the track containing the sort after LBA, it talks about bringing the sort after
       LBA (and a given number of blocks) into the disk's cache. Also  the  PRE-FETCH  commands  have  an  IMMED
       field.

       The  PRE-FETCH commands can report "real" errors but usually they will report one of two "good" statuses.
       To do this they return the rarely used CONDITION MET status. If the number of blocks does actually fit in
       the  cache  (when  IMMED=0)  or there is enough room in the cache when the command arrives (when IMMED=1)
       then a CONDITION MET status is returned. If the requested number of blocks did not fit (IMMED=0) or would
       not  fit  (IMMED=1)  then  status  GOOD is returned. So if a disk has a large cache and PRE-FETCH is used
       sparingly then the command is more likely to return CONDITION MET than  GOOD.  This  presents  some  SCSI
       sub-systems  with  problems  as due to its rareness they mishandle CONDITION MET and treat it as an error
       (see NOTES section below).

OPTIONS

       Arguments to long options are mandatory for short options as well.

       -T, --10
              use a 10 byte cdb command, either SEEK(10)  or  PRE-FETCH(10)  command.  In  the  absence  of  the
              --pre-fetch  option, the SEEK(10) command is used. If the --pre-fetch option is given without this
              option then a PRE-FETCH(16) command is used.

       -c, --count=NC
              NC is the number of commands (one of  SEEK(10),  PRE-FETCH(10)  or  PRE-FETCH(16))  that  will  be
              executed.  The  default value is 1. If an error occurs it is noted and the program continues until
              NC is exhausted.  If NC is 0 then options are checked and the DEVICE is opened but no commands are
              sent.

       -g, --grpnum=GN
              GN  is  the  group  number,  a value between 0 and 63 (in hex: 0x3f). The default value is 0. This
              option is ignored if the selected command is SEEK(10).

       -h, --help
              output the usage message then exit.

       -i, --immed
              this option only applies to PRE-FETCH(10) and PRE-FETCH(16), setting the IMMED bit.  Without  this
              option,  the  DEVICE  returns  after  it has completed transferring all, or part of, the requested
              blocks into the cache. If this option is given the DEVICE returns after it has done sanity  checks
              on the cdb (e.g. making sure the LBA is greater than the number of available blocks) and before it
              does the transfer into the cache.
              Note that even when this option is given, the return status from the PRE-FETCH commands  is  still
              either  CONDITION  MET status (if the cache seems to have enough free space for the transfer) or a
              GOOD status (if the cache does not seem to have enough free space).

       -l, --lba=LBA
              LBA is the starting logical block address that is placed in the command descriptor block (cdb)  of
              the  selected command. Note that the LBA field in SEEK(10) and PRE-FETCH(10) is a 32 bit quantity,
              while with PRE-FETCH(16) it is a 64 bit quantity. The default value is 0 .

       -n, --num-blocks=NUM
              NUM is the number of blocks, starting at and including LBA, to place in the  DEVICE's  cache.  The
              SEEK(10) command does not use the NUM value. For PRE-FETCH(10) NUM is a 16 bit quantity, while for
              PRE-FETCH(16) it is a 32 bit quantity. The default value is 1 . If NUM is 0 then the  DEVICE  will
              attempt to transfer all blocks from the given LBA to the end of the medium.

       -p, --pre-fetch
              this  option selects either PRE-FETCH(10) or PRE-FETCH(16) commands. With the --10 also given, the
              PRE-FETCH(10) command is selected; without that option PRE-FETCH(16) is selected. The default  (in
              the absence of this and other 'selecting' options) the SEEK(10) command is selected.

       -r, --readonly
              this  option  sets a 'read-only' flag when the underlying operating system opens the given DEVICE.
              This may not work since operating systems can not easily determine whether  a  pass-through  is  a
              logical  read  or  write  operation  so they take a risk averse stance and require read-write type
              DEVICE opens irrespective of what is performed by the pass-through.

       -s, --skip=SB
              SB is the number of logical block addresses to skip, between repeated commands when NC is  greater
              than  1.  The  default value of SB is 1 . SB may be set to 0 so that all NC PRE-FETCH commands use
              the same LBA.

       -t, --time
              if given the elapsed time to execute NC commands is recorded. This  is  printed  out  before  this
              utility exits. If NC is greater than 1 then the the "per command" time is also printed.

       -v, --verbose
              increase the level of verbosity, (i.e. debug output).

       -V, --version
              print the version string and then exit.

       -w, --wrap-offset=WO
              WO  is  the  number of blocks, relative to LBA, that when exceeded, set the next command's logical
              block address back to LBA. Whether this "reset-to-LBA" action occurs depends on the values NC  and
              SB.

NOTES

       Prior  to  Linux kernel 4.17 the CONDITION MET status was logged as an error.  Recent versions of FreeBSD
       handle the CONDITION MET status properly.

       If either the --count=NC or --verbose option is given then a summary line like the following is output:

           Command count=5, number of condition_mets=3, number of goods=2

       before the utility exits.

EXIT STATUS

       The exit status of sg_seek is 0 (GOOD) or 25 (CONDITION_MET) when this utility is successful. If multiple
       commands  are  executed  (e.g.  when  NC  is greater than 1) then the result of the last executed SEEK or
       PRE-FETCH command sets the exit status. Otherwise see the sg3_utils(8) man page.

AUTHORS

       Written by Douglas Gilbert.

REPORTING BUGS

       Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT

       Copyright © 2018 Douglas Gilbert
       This software is distributed under a FreeBSD license. There is NO warranty; not even for  MERCHANTABILITY
       or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO

       sg_vpd(sg3_utils); sdparm(sdparm)