High Capacity DASD Dual-Copy Secondary to Multiple 3390 Primary Devices

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IP.com Disclosure Number: IPCOM000112750D
Publication Date: 01-Jun-1994
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Publishing Venue

IBM Technical Disclosure Bulletin (TDB v37 n6A 06-94 p493-498)

Related People

Cord, JH - Author [+2] [-2]
Tucson
Hartung, MH - Author
Tucson
Michod, CS - Author
Tucson

Abstract

A method to allow a single High Capacity DASD device to act as a Dual-Copy secondary device to a multiplicity of smaller 3390 devices (i.e., models 2 and 3, in particular) is disclosed.

Language

English (United States)

Country

United States

Document File

6 pages / 261.7 KB

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 20% of the total text.

High Capacity DASD Dual-Copy Secondary to Multiple 3390 Primary Devices

      A method to allow a single High Capacity DASD device to act as
a Dual-Copy secondary device to a multiplicity of smaller 3390
devices (i.e., models 2 and 3, in particular) is disclosed.

      The High Capacity DASD device has a user data or track capacity
equal to three 3390-3 devices or four 3390-2 devices.  It would be of
value if the High Capacity DASD could act as a secondary Dual-Copy
device to multiple 3390 primary devices when executing the Dual-Copy
algorithm.  Presently, it lacks that capability.

Notes

1.  This disclosure requires the reader to have some familiarity with
    3990-3 algorithms and functions, in particular that of Dual Copy.

2.  Some acronyms are used repeatedly in this disclosure:

    o   DASD: Direct Access Storage Device

    o   CCHH: Cylinder (CC), Head (HH) address: the address of the
        desired device track

      Description - High Capacity DASD Dual-Copy Secondary allows
several 3390 primary devices to share a High Capacity DASD secondary
device by allocating a logical 3390 secondary, of the same model as
the primary, on to the High Capacity DASD secondary, for each primary
volume requesting space and for which space is available.

      Space on the High Capacity DASD volume is allocated
contiguously for each 3390 primary, and the entire user (i.e.,
primary) track space of the 3390 primary volume is allocated on the
High Capacity DASD secondary.  The  allocation capacity of the High
Capacity DASD is three 3390-3 primary volumes or four 3390-2 primary
volumes.  3390-1 primary volumes are not supported (for performance
reasons), nor are mixtures of 3390-2 and 3390-3 primary volumes.

The characteristics of the High Capacity DASD Dual-Copy Secondary are
as follows:

o   For each 3390 primary volume which is a member of a set of such
    volumes which will use a particular High Capacity DASD as a
    secondary volume, an offset to the origin of the 3390's 0
    cylinder on the High Capacity DASD is stored in a table in the
    subsystem.  This offset is keyed by the 3390's device Unit
    Address.

o   The list of device Unit Addresses and their offsets is created as
    a by-product of the execution of Establish Duplex Pair, 3990
    function.  Establish Duplex Pair will copy one 3390 at a time,
    offsetting its origin correctly on the High Capacity DASD
    secondary.  Establish Duplex Pair must be executed separately for
    each of the 3390 volume copies to the High Capacity DASD
    secondary.  The Establish Duplex Pair flag byte indicates if
    multiple 3390s are to be copied to the High Capacity DASD device.
    If the flag byte isn't so set, Establish Duplex Pair will create
    a single primary with a High Capacity DASD as secondary.  In the
    case of multiple primary devices to a single High Capacity DASD
    secondary d...

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