-+------------------------------------------------------------------+-
    openbsd and a scsi-tower
-+------------------------------------------------------------------+-

this is written coz i fighted my tiny openbsdbox quite some time
to handle the scsi-tower with its 6x2gig discs the way i wanted.

situation:

  _____
  |sd0|
  |  1|
  |  2|
  |  3|
  |  4|      ___________
  |  5|      |devil|sd6|
  ======-----===========

sd0-5 are 6x2gig dec-scsis-discs, plan is to use them for regular
backups of my stuff, should be big enough to handle this. the box
(devil) itself is running openbsd3.5 on a pentium128 with 128megs
of ram.

sometimes i use this machine just for surfing (console mode) when
my gf uses my machine. so i dont want to have the scsi-tower ALWAYS
enabled at boottime, sometimes i want to enable it at runtime,
store the stuff, sync everything and disable the scsi-tower again.

so here is how to do this:

 1. teach the kernel how to number things right.

   in default mode the kernel assumes the first found disc
   is /dev/sd0 and so on. that might be true in most cases but
   not in this one.

   i want have  bus0 target0 lun0 always be /dev/sd0 and target6
   should be /dev/sd6. otherwise the system has problems with
   booting since the (internal) 4gig-disc on target6 becomes
   /dev/sd0 if the tower is off and /dev/sd6 if the tower is
   enabled. this sux :)

   so:

      config -e /bsd -o /bsd.scsi

   and wire down the entries for the scsi-discs. when you are in
   the config-console type "help" and use the "change" command
   to do the things. perhaps you need "add" too for adding the
   specific entries. i removed every unneeded scsi-stuff from the
   kernel and put (for example) ahc0 to scsibus0.

   try out that new kernel and see if devices remain the same if
   booted with enabled/disabled scsi-tower

 2. boot the machine with scsi-tower off.

 3. switch the scsi-tower on, wait till it gets completly ready.

 4. enter:

     scsi -f /dev/rsd6c -r

   to rescan the bus. the kernel should now recognize the 
   new discs and connect the hardare to the right "/dev"-entries.

   you need to run the command on a working scsi device otherwise
   you ll get an io-error. some docs say something about /dev/scsi 
   but till now i didnt figure out how to enable this super-device.

 5. to disable the discs:

     scsi -f /dev/rsd0c -v -c "1b 0 0 0 0 0"

   for each disc. this results in some errors from the kernel but
   it worked and the discs spin down. after that you can turnoff
   your scsi-tower.

   a final 

     scsi -f /dev/rsd6c -r

   shoould bring the kernel in sync with the current situation.


happy scsiing,

  mathias(akira)