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Browse Prior Art Database

Destage Algorithm Transitions with Redundant Arrays of Independent Disks

IP.com Disclosure Number: IPCOM000116677D
Original Publication Date: 1995-Oct-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Legvold, V: AUTHOR [+3]

Abstract

A method to transition between Synchronous and Asynchronous communication between a Control Unit with a cache and Non-Volatile Store (NVS) and a RAID drawer with an NVS is disclosed.

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

Destage Algorithm Transitions with Redundant Arrays of Independent
Disks

      A method to transition between Synchronous and Asynchronous
communication between a Control Unit with a cache and Non-Volatile
Store (NVS) and a RAID drawer with an NVS is disclosed.

The subsystem has three operating modes:

Asynchronous Commit
    In this mode the data is deleted from the control unit NVS when
     the data has been successfully transferred to the drawer Cache.
     A copy remains in the control unit Cache until the data has been
     successfully transferred from the drawer Cache to the HDAs.  In
     addition, a control record is stored in the control unit NVS
     prior to deleting the control unit NVS copy of the data and is
     deleted when the data is written to the HDA.  If the data
     transfer from the drawer Cache to the HDAs is not successful,
     the data in the drawer Cache is purged for the failing track and
     the failing track will be transferred from the control unit
     cache again.

Synchronous Commit
    In this mode the data is not deleted from the control unit NVS
     until the data has been successfully written to the HDAs.  If
     the data cannot be successfully written to the HDAs, the data in
     the drawer for all tracks is purged and all tracks are
     transferred from the control unit cache again.

Pending Synchronous Commit
    This is the transition from Asynchronous to Synchronous Commit
     Mode.  All data previously written to the drawer must be
     destaged to the HDAs before the transition is complete.

      A Control Word is defined and initialized, in Shared Memory,
for each device.  A zero Control Word indicates that the Asynchronous
Commit operating mode will be used for the device.  Each reason that
requires Synchronous Commit mode is assigned a flag in the control
word.
  o  Subsystem Cache unavailable
  o  NVS unavailable
  o  DFW off
  o  Device caching off
  o  Device has pinned retriable data
  o  Battery failed
  o  Fan failed

      The functions in the control unit that monitor the state of the
resources will set the appropriate...