Browse Prior Art Database

Dynamic Volume Table of Contents Detection

IP.com Disclosure Number: IPCOM000110891D
Original Publication Date: 1994-Jan-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Day, K: AUTHOR [+3]

Abstract

A method to dynamically detect Volume Table of Contents (VTOC) data on Extended Count Key Data Optical Disks.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 73% of the total text.

Dynamic Volume Table of Contents Detection

      A method to dynamically detect Volume Table of Contents (VTOC)
data on Extended Count Key Data Optical Disks.

      In the 370 Input/Output Direct Access Storage Device (DASD)
architecture, the channel communicates with the DASD control unit by
writing and reading Extended Count Key Data (ECKD) records.  The
control unit has no knowledge of what type of data is contained in
user records on the DASD.  Some of the data is the Volume Table Of
Contents for the particular DASD volume.  The VTOC data will very
likely be frequently accessed.  If this data could be detected by the
DASD control unit, the control unit could then treat this data as
special (such as with the use of a cache) and give it higher
performance.  This could result in significantly higher performance
of the storage subsystem.  This article describes a technique for
recognizing VTOC data.

      When optical DASD is attached to 370 channels, using the ECKD
architecture, detection of VTOCs is very important given the
relatively poor performance of the optical device when compared to
magnetic DASD.

      VTOCs have a unique record structure.  The idea is to use this
knowledge of this unique record structure to detect the presence of a
VTOC and then exploit it appropriately.  VTOC records are composed of
a 44-byte key field and a 96-byte data field.

      Microcode can detect (see algorithm below) these unique
attributes and then "labe...