Browse Prior Art Database

No Modified Data Indicator for Caching Subsystem

IP.com Disclosure Number: IPCOM000101260D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 78K

Publishing Venue

IBM

Related People

Beardsley, BC: AUTHOR [+3]

Abstract

A cached DASD subsystem that allows write operations to complete without updating the DASD (Non-Retentive Data, Fast Write and Dual Copy) has to assume, if the non-volatile storage is not available at IML (Initial Microprogram Load), that all volumes that were operating in that manner are down-level unless an indicator is provided to show that the subsystem was shut down in an orderly manner and all DASD was updated.

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

No Modified Data Indicator for Caching Subsystem

       A cached DASD subsystem that allows write operations to
complete without updating the DASD (Non-Retentive Data, Fast Write
and Dual Copy) has to assume, if the non-volatile storage is not
available at IML (Initial Microprogram Load), that all volumes that
were operating in that manner are down-level unless an indicator is
provided to show that the subsystem was shut down in an orderly
manner and all DASD was updated.

      The No Modified Data indicator is a flag kept in a non-volatile
storage that can be checked by an IMLing Storage Path to determine if
all DASD volumes were up-to-date when the subsystem went down.  When
the non-volatile storage is unavailable at IML, this indication
allows the subsystem to make all volumes available without a data
integrity exposure.  Without this indication all Fast Write and Dual
Copy volumes would have to be assumed to be down-level.  Fast Write
access would receive Unit Check, and Dual Copy volumes would be made
Failed Duplex.  Also with this indication the Subsystem Storage is
made available without stepping the NRDID (Non-Retentive Data
Identifier), allowing non- retentive access to continue with the
previous ID.

      The "No Modified Data" indication is used at IML to indicate
that there was no data accepted for DASD that is not on DASD.

      The indicator is set following the successful destage of all
modified data initiated by a Perform Subsystem Function command
specifying a "Destage Modified Tracks" order.  This order initiates a
destage of all modified tracks in cache by making a single pass
through the cache directory and scheduling the transfer from cache to
DASD of all records that have been modified in cache and not yet
updated on DASD.  A pending indicator is set in the JAS storage (a
volatile storage array readab...