Browse Prior Art Database

SCSI Switch for Redundant Arrays

IP.com Disclosure Number: IPCOM000122246D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Floryance, GG: AUTHOR

Abstract

Disclosed is a method of isolating two SCSI initiators sharing the same SCSI bus in a redundant array using a SCSI switch. This method provides improved throughput during normal operation while providing redundancy in the event that one of the initiators becomes disabled.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 60% of the total text.

SCSI Switch for Redundant Arrays

      Disclosed is a method of isolating two SCSI initiators
sharing the same SCSI bus in a redundant array using a SCSI switch.
This method provides improved throughput during normal operation
while providing redundancy in the event that one of the initiators
becomes disabled.

      One popular SCSI redundancy configuration provides a primary
and a backup initiator on the same bus.  Increased performance of the
redundant SCSI array is achieved by eliminating the backup initiators
and dividing the DASD devices or disk drives into two separate
groups, each with its own primary initiator.  Redundancy is achieved
through use of a switch which isolates each initiator during normal
operation but which can connect two SCSI buses in the event an
initiator fails.

      The example in the figure illustrates the switch bus
configuration.  Array host adapter A contains four initiators S-V at
SCSI device addresses zero or one.  Each initiator communicates over
a SCSI bus with three DASD devices whose device addresses are either
all odd (3,5,7) or all even (2,4,6) in correspondence with the
initiator ID.

      During normal operation, the switch is inactive and the ratio
of three devices per SCSI initiator exists.  However, if initiator S
fails, switch J can be closed and initiator W can take over the
workload for initiator S.  Note that the degraded mode bus now
contains six unique DASD devices (2-7) connected to initiator W.

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