SUMMARY : SCSI adresses

From: Eckhard Rueggeberg (
Date: Wed Sep 25 1991 - 12:24:51 CDT

The original question was where the sd1 and sd3 boot messages
come from and are for on a VME bus machine.
Well, the explanation is in the sd(4) man page.

kevins@Aus.Sun.COM (Kevin Sheehan {Consulting Poster Child}) said :

  What the kernel notices on the SCSI bus bus is entirely a function of
  what you tell it in the config file (for this machine anyway)

  Things on the SCSI bus have a target ID and Logical Unit Number - each
  controller lives at an address (the Sun host adaptor takes address 7) and
  can have up to 8 units attached to each controller. The old Sun
  shoeboxes could have two disks on a controller, so Sun default is to
  map each target ID *2to the unit #, leaving the odd unit numbers for
  the other logical unit.

  The mapping is completely arbitrary (as a quick look at the sun4c machines
  will show - unit 0 is ID 3 there) and is up to you alone.

  Entires for the non-sun4c machines are of the form:

  [disk|tape|device] [sd|st|XX]# at <controller> drive <drive #> flags <type>

  controller refers to the SCSI host adaptor (like si0, sm0, sw0, se0) and
  the drive number is target*8 + lun. Since config takes numbers in octal,
  it is much easier to specify them that way. The flags entry is acutally
  an index into a table for the proper device subroutines. 0 is for disk
  1 for tapes, 2 for CD, &c.


  disk sd0 at si0 drive 000 flags 0 # ID 0, lun 0
  disk sd2 at si0 drive 010 flags 0 # ID 1, lun 0
  disk sd3 at si0 drive 020 flags 0 # ID 2, lun 0
  disk sd4 at si0 drive 021 flags 0 # ID 2, lun 1
  tape st0 at si0 drive 040 flags 1 # ID 4, lun 0
  device kk0 at si0 drive 050 flags 4 # user device w/different driver
  The sun4c machines differ, in that they have target and lun fields
  specified explicitly. (Alexander Dupuy) said :

  Back before every disk came with a SCSI controller built in, you could get a
  SCSI controller which had an ESDI or ST-506 interface to which you could attach
  one or two drives. These were the old Sun-3 "shoebox" units; the ST-506
  controller was made by Adaptec, and the ESDI controller was the Emulex MD-21.
  If you look at a sun4c kernel config file, you'll see that ina addition to the
  "target" keyword, there is a "lun" (logical unit) keyword; you can have up to
  eight logical units per SCSI target. In the sun4 kernel config file, the second
  octal digit in the "slave" number is the "target" and the last digit is
  the "logical unit"; thus sd1 and sd3 are lun 1, while all the others are lun 0.

  So the answer to your question is that no, you can't add any more disks, at
  least unless you remove one of the tape drives. You could get a shoebox with
  an Adaptec ST-506 and hang two slow, low capacity disks in the place of one of
  your existing ones, by why would you want to? (Steve Jay) said :


  If you want to put more SCSI devices on your system, you need another
  SCSI adapter (si1) in your system. They cost around $1500 in the USA.
  It works fine....we have a machine with 2 SCSI adapters, each with four
  disks, an Exabyte, and a CD drive.

Thanks also to

Hans van Staveren <>
Mike Raffety <>
philica!geertj (Geert Jan de Groot)
trdlnk! (Michael Sullivan)

Eckhard R"uggeberg
Mathematisches Institut der Universit"at G"ottingen
Bunsenstr. 3 - 5
3400 G"ottingen

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