phpman > man > sg_seek(8)

SG_SEEK(8)                                    SG3_UTILS                                   SG_SEEK(8)



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 re‐
       quested 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 prob‐
       lems  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 pro‐
              gram continues until NC is exhausted.  If NC is 0 then options are checked and the DE‐
              VICE 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  re‐
              turns  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  com‐
              mands  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 se‐
              lected. 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 be‐
              fore 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 com‐
              mand'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 MER‐
       CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO
       sg_vpd(sg3_utils); sdparm(sdparm)



sg3_utils-1.43                             September 2018                                 SG_SEEK(8)