Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Technique for Logically Altering SCSI Device Addresses

IP.com Disclosure Number: IPCOM000099776D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 4 page(s) / 102K

Publishing Venue

IBM

Related People

Gorder, WH: AUTHOR [+3]

Abstract

Described is a technique for logically altering a Small Computer System Interface (SCSI) device's address. The technique requires devices on an SCSI bus to support a vendor unique command. (In SCSI, a vendor unique command is a command that is not an SCSI mandatory or optional command, and does not use a reserved operation code.) The vendor unique command is used to reassign a device's hardware address to a logical address. Load balancing and performance tuning of devices on an SCSI bus are difficult within normal SCSI protocol. The technique alters a preferential SCSI treatment during bus arbitration to help achieve these goals. The technique also circumvents addressing restrictions in a host AS/400*.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Technique for Logically Altering SCSI Device Addresses

       Described is a technique for logically altering a Small
Computer System Interface (SCSI) device's address.  The technique
requires devices on an SCSI bus to support a vendor unique command.
(In SCSI, a vendor unique command is a command that is not an SCSI
mandatory or optional command, and does not use a reserved operation
code.)  The vendor unique command is used to reassign a device's
hardware address to a logical address.  Load balancing and
performance tuning of devices on an SCSI bus are difficult within
normal SCSI protocol.  The technique alters a preferential SCSI
treatment during bus arbitration to help achieve these goals.  The
technique also circumvents addressing restrictions in a host AS/400*.

      The SCSI is an American National Standard (X3.131-1986).
SCSI-2 is an extension to SCSI, and is a proposed standard.
Reference is made to SCSI without distinction between the two.

      A minimum requirement of an SCSI vendor unique command is to
transform a set of up to eight devices with unique addresses set in
hardware to the same set of devices with unique logical addresses.
The logical addresses may be different from the hardware addresses.
Note that SCSI requires unique addresses.

      There are only eight addresses and a potential for eight
devices.  Addresses are unique and must be changed in a sequential
fashion.  To accommodate these requirements, the vendor unique
command has the following features:
      -    It must be accepted by a device when that device
           is selected with its current address.
      -    It must specify an SCSI address which the device
           uses from this point on.
      -    It must specify (or imply) a time delay during
           which this device does not respond to selection.

      The time delay, above, is necessary to maintain unique
addresses during the period of time that addresses are being
reassigned.  After the transition period, the SCSI bus once again has
a complement of devices with unique addresses.

      A look at the SCSI bus from power-up time until address
reassignments are complete is shown below.
   -    System and devices power up and come ready (Fig. 1).
      - ...