Browse Prior Art Database

Shared Small Computer System Interface Protection Mechanism

IP.com Disclosure Number: IPCOM000118402D
Original Publication Date: 1997-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 81K

Publishing Venue

IBM

Related People

Benayoun, A: AUTHOR [+3]

Abstract

Disclosed is a method of sharing Small Computer System Interface (SCSI) devices such as hard disks between two devices, one being the active one, the second being the backup in case of failure of the first one: both may have the same SCSI address.

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

Shared Small Computer System Interface Protection Mechanism

      Disclosed is a method of sharing Small Computer System
Interface (SCSI) devices such as hard disks between two devices, one
being the active one, the second being the backup in case of failure
of the first one:  both may have the same SCSI address.

      State of the art - SCSI allows multi-master mode but without
protection and each device should have a unique address.  It means
that there is no way to prevent one master device to access the same
data used by the other master device which may result, in case of
failure of one master, in data corruption.

      Summary and advantage of the proposed mechanism - Two control
leads of the SCSI cable are monitored through a special mechanism to
prevent one device to access the SCSI bus when the other has granted
the bus for its own purposes.  In case of failure of the latter, the
backup device will get the access to that bus while the failing
device will be locked.

This offers:
  o  a high protection level
  o  a full redundancy using a single database.  This database
      can also be duplicated (mirroring) and both normal and
      mirror disks may be used by the master and the backup
      devices but not simultaneously.
  o  A solution for redundant systems willing to share a single
      database.

      Proposed solution - The objective is to have two initiator
devices on the Bus, one being active while the second is the backup
devices used when the active fails.

      When the active is defined, the SCSI bus is protected from any
attempt from the backup device.

      The active Initiator device can, in that case, store the
database in the hard disks (target devices), which can be reused by
the backup initiator de...