man > scsi-config(8)

scsi-config(8)                          Scsiinfo User's Guide                         scsi-config(8)

NAME
       scsi-config - query information from a scsi device with a nice user interface

SYNOPSIS
       scsi-config [device]

DESCRIPTION
       scsi-config queries information from an scsi target with a nice Tcl/Tk user interface. If you
       do  not  specify  a  device  to query, scsi-config calculates a list of available devices and
       prompts it to you.

       By the nature of a graphical user interface, most things will explain them  self.  Basically,
       scsi-config shows a list of buttons for certain mode pages which you may press. Those buttons
       which  you  can  press and the text windows with white backgrounds can be modified by you and
       the modifications send back to the device.

       In the main window there is a button to instruct the device to save  the  data  in  some  non
       volatile  memory  (if  it  supports  it). Note that this will instruct the device to save the
       Read-Write Error Recovery Page , Disconnect-Reconnect Page , Format  Device  Page  ,  Caching
       Page , and Control Mode Page in its NVRAM. Usually saving even a single of those should write
       them all to the NVRAM, but you never know.

       You  can query the current, the factory default and the values in the NVRAM (which may not be
       the current parameters) from the device.

       Not all combinations of button toggles or all values are valid. In general, try to  set  them
       and see which values the drive accepts.  scsi-config rereads the device configuration immedi‐
       ately, s.t. you see which values where accepted.

       Also  note  that  some disk drives are notched, and that those have an active notch (shown in
       the main window) to which all your settings apply (at least those of notched pages, which are
       also marked in slate gray). You can select the active notch to which your settings apply (and
       to which the values refer) in the Notch Page.

       For those devices which do not feature an NVRAM (generally removable media devices) and as  a
       kind  of  backup,  you  can  save the current settings to a file. Actually the file will be a
       /bin/sh script making the necessary scsiinfo(8) calls to set the saved parameters  when  exe‐
       cuted.

       There  is  also  a nice Overview button which will query many details about the disk geometry
       and draw them in a nice picture. This looks esp. nice for drives with many notches,  that  is
       different regions on the disk with different tracks per sector settings. It is also very use‐
       ful for notched drives as you can immediately select the mode pages for each notch.


SOME USAGE GUIDELINES
       1. General Warning
              Generally, do not modify settings you don't understand. It is useful to know the SCSI-
              II  specs  mentioned below. Some setting may render the device unusable or even damage
              it. Usually a power cycle resets the state (if you do not save the weird  settings  in
              the  NVRAM). Some settings affecting the assignment of logical sectors will render the
              disk unusable until the next low level format.

       2. On Write Caching
              As an old warning, this does also mean you should not generally switch the write cache
              on.  At least on those drives where you have a choice at all. Reasons are twofold:

              a)     It is a priori unclear when the drive will actually perform the writes. This is
                     a bad thing when considering shutdown of your machine. On the  other  hand,  it
                     seems  sensible  to  assume that the drive will immediately write it's cache to
                     disk when it is idle (after all file systems are unmounted) and due to the size
                     of the on disk cache this will usually only need a few seconds after the  shut‐
                     down  (but  the  drive lamp will usually not glow, as it is mostly connected to
                     the host adapter (if you have a lamp at all) and it is not participating).

                     There is a SCSI command to flush the caches. Linux could call it prior to shut‐
                     ting down, spinning a disk down. Due to my  knowledge  this  is  not  yet  done
                     though.

              b)     As the writes are performed asynchronously, errors are reported asynchronously.
                     The  disk  might  return  an error at some simple read instruction related to a
                     write which was acknowledged OK several transactions ago. This  generally  con‐
                     fuses  things  and  makes  interpreting errors very difficult. Some devices are
                     known/said to not report write errors in this mode of operation at all.

                     Just imagine that at the point where a file system is unmounted, or a  new  re‐
                     movable  media is detected it could tell: Oops, BTW, there was some write error
                     ago although I told you it was OK already.


              Thus, when you run a disk in write cache mode, keep it in mind when weird  error  mes‐
              sages  occur  and  give  the disk time to flush it's buffers at shutdown. Generally it
              would be good if you knew more vendor specific details on how the disk operates in the
              write cache mode.


       3. Reassigning Bad Blocks Automatically
              One of the nice features of SCSI disk is that they allow to remap bad blocks automati‐
              cally as they are detected without any user intervention. However, you  actually  have
              to  enable  this  feature!   It turned out that you can not generally assume a disk in
              this mode. To enable this mode or check the settings, proceed as follows:

              a)     Go to the Read-Write Error Recovery Page.  AWRE (Automatic  Write  Reallocation
                     Enable)  and ARRE (Automatic Read Reallocation Enable) buttons enable the auto‐
                     matic reallocation.

                     In the same window, you can select the maximal retries  performed.  EER  allows
                     the  disk to do some Early Error Recovery which is fast (but might misdetect or
                     miscorrect data).  A selected DCR button (Disable CoRrection  Codes)  disallows
                     the  disk to use any error correction codes at all (thus the drive will have to
                     retry until it performs an error free read).

                     Usually a sector will be reallocated after even a  single  read  retry  or  the
                     given  number  of failed write retries. When the sector cannot be recovered, it
                     is reallocated but the data is lost and an error is signalled.

                     The other buttons there apply to error reporting as well. TB Transmits the  bad
                     Block  together  with the error, RC Reads Continuous, that is, does not pause a
                     read operation while retrying or using error code calculations to recover a bad
                     block (thus may return bad data). PER lets the disk report even  recovered  er‐
                     rors  (Post  ERror), DTE (Disable Transfer on Error) even breaks a running data
                     transmission when an error is detected.


              b)     Even when the reallocation is enabled, the disk must  actually  have  some  re‐
                     served  areas where to remap the bad blocks. The Format Page controls this. Ei‐
                     ther a given number of Alternate Sectors Per LUN is set  aside  for  the  whole
                     disk  or  a  given number of tracks is defined to be a zone and for each zone a
                     number of sectors or tracks is put aside.  These alternate data areas are where
                     bad sectors are remapped.

                     Note that this page is very likely to apply only to  the  current  notch  on  a
                     notched disk device.

                     If  there are no, or not many alternate sectors reserved on your disk, you must
                     change these settings.

                     I found that those disks which allow to modify these settings  are  very  often
                     set  to  no reserved sectors at all by the vendors, as this increases the disks
                     capacity. For the sake of stability, you should really modify these settings.

                     If you decide to modify the number of alternate sectors, you must

                     i)     Save the parameters to the NVRAM of the disk.

                     ii)    Low-level format the disk drive (and not erase the NVRAM during this op‐
                            eration).

                     to make the changes be effective.


              c)     Esp. when you set the disk to not report recovered errors (or when it is  in  a
                     write cache mode or something), and just as a general guideline, keep an eye on
                     the grown defects list where the disk will report all the remappings which took
                     place as your disk ages.

                     The  old adventurers guide line applies: Save (Backup) Early, Save (Backup) Of‐
                     ten. Find the right time to replace your disk avoiding too much work recovering
                     your data.


BUGS
       scsi-config could be enhanced by making better use of Tcl/Tk. I learned much about it  during
       my  work  on  tk_scsiformat(8)  and their would be much room for fixes and enhances. On other
       hand, it fulfils it's purpose as it is quite nicely already.

       As scsi-config makes heavy use of scsiinfo(8) all it's bugs (esp. on defect reading) apply.


FILES
       /usr/lib/scsi/cache,  /usr/lib/scsi/control,  /usr/lib/scsi/disconnect,  /usr/lib/scsi/error,
       /usr/lib/scsi/format,   /usr/lib/scsi/generic,   /usr/lib/scsi/inquiry,  /usr/lib/scsi/notch,
       /usr/lib/scsi/overview,  /usr/lib/scsi/peripheral,  /usr/lib/scsi/rigid,  /usr/lib/scsi/save-
       changes,  /usr/lib/scsi/save-file,  /usr/lib/scsi/tworands, /usr/lib/scsi/verify (Tcl/Tk sub‐
       routines used by scsi-config).
       /dev/sd*
       /dev/sg*
       /dev/scd*
       /dev/st*
       /dev/nst*
       /dev/rmt*
       /dev/nrmt*


SEE ALSO
       scsiinfo(8), scsiformat(8), tk_scsiformat(8), fdisk(8), sd(4),

       Draft proposed
       American National Standard
       for information systems

       SMALL COMPUTER SYSTEM INTERFACE - 2
       (SCSI-2)

       MARCH 9, 1990


AUTHORS
       Eric Youngdale.
       Michael Weller <eowmob AT exp-math.de>, Versions 1.5 & 1.7

scsiinfo 1.7                               24 August 1997                             scsi-config(8)