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

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

       scsi-config [device]

       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 gen-
       eral,  try  to  set them and see which values the drive accepts.  scsi-
       config rereads the device configuration immediately, 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  set-
       tings  to a file. Actually the file will be a /bin/sh script making the
       necessary scsiinfo(8) calls to set the saved parameters when executed.

       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
       useful for notched drives as you can immediately select the mode  pages
       for each notch.

       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  set-
              tings  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 per-
                     form 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 sys-
                     tems are unmounted) and due to the size of  the  on  disk
                     cache this will usually only need a few seconds after the
                     shutdown (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 shutting 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 gener-
                     ally confuses 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 removable 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 messages 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 automatically 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  (Auto-
                     matic Write Reallocation Enable) and ARRE (Automatic Read
                     Reallocation Enable) buttons enable the automatic reallo-

                     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  opera-
                     tion  while  retrying or using error code calculations to
                     recover a bad block (thus may return bad data). PER  lets
                     the  disk  report even recovered errors (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 reserved areas where to remap the  bad
                     blocks.  The  Format  Page  controls this. Either 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 sec-
                     tors 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 set-
                     tings 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

                     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 operation).

                     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 remap-
                     pings which took place as your disk ages.

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

       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 pur-
       pose as it is quite nicely already.

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

       /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 subroutines used by scsi-config).

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

       Draft proposed
       American National Standard
       for information systems


       MARCH 9, 1990

       Eric Youngdale.
       Michael Weller <eowmobATexp-math.de>, Versions 1.5 & 1.7

scsiinfo 1.7                    24 August 1997                  scsi-config(8)