Browse Prior Art Database

Multiple Path Storage Director

IP.com Disclosure Number: IPCOM000100378D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 88K

Publishing Venue

IBM

Related People

Beardsley, BC: AUTHOR [+5]

Abstract

A method to resolve system error recovery problems related to the use of multiple storage paths per storage director within the storage subsystem control unit, is performed by assigning a unique control unit address with respect to each of the connected channels. Each storage path within the same storage director has its own switch and daisy chain bus connected to the same channels and devices, respectively. Each storage path can intercept and execute any system input/output issued to the storage director through the connected channels when the storage path is free.

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

Multiple Path Storage Director

       A method to resolve system error recovery problems
related to the use of multiple storage paths per storage director
within the storage subsystem control unit, is performed by assigning
a unique control unit address with respect to each of the connected
channels.  Each storage path within the same storage director has its
own switch and daisy chain bus connected to the same channels and
devices, respectively. Each storage path can intercept and execute
any system input/output issued to the storage director through the
connected channels when the storage path is free.

      For fencing, a storage subsystem with multiple storage paths
per storage director, is required to keep track of the amount of
unrecovered equipment check errors encountered by any subsystem
resource with respect to a resource access path  while that resource
takes part in processing a channel command word chain.  Also, the
storage subsystem is required to determine if the resource should be
fenced off, that is, logically disconnected from that storage path,
when the error rate for resource exceeds a predetermined threshold
limit.  After being fenced off, the resource cannot be selected nor
participate in the processing of any system input/output chain
through that resource access path.

      A common structure shared by all storage directors within a
storage subsystem allows the storage directors to communicate with
each other.  All of the storage paths within the storage director
bear identical connectivity to channels and devices connected to the
storage director.

      To solve the error problems for the concept of multiple storage
paths per storage director, the control unit performs error recovery
for all types of errors.  The storage path has to keep track of the
equipment checks for uncorrectable data check errors which occurred
on all types of subsystem resources.  The error rates for each
resource with respect to each storage path, are kept in counters.
When the error rate for any such subsystem resource exceeds its
threshold limit, that resource may be considered to be fenced off
from the access sto...