Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Emulating a Shared DASD Device in Expanded Store on ES/9000 Class Systems

IP.com Disclosure Number: IPCOM000104160D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 2 page(s) / 78K

Publishing Venue

IBM

Related People

Calta, SA: AUTHOR [+2]

Abstract

Disclosed is a potential LIC feature designed to exploit the large amounts of Expanded Storage available on ES/9000* class systems. This "Virtual Disk" feature enables applications to access the system Expanded Storage utilizing any existing DASD software written for any specific DASD device type (eg. 3380 or 3390 DASD Subsystems). Thus, exploitation of expanded storage by applications does not require any special access method, or changes to the applications. The Virtual Disk can be dedicated to a single system or the design can incorporate the option to share Virtual Disks across multiple systems. By designing the Virtual Disks to emulate a DASD subsystem that is already known to software, it takes on the appearance of a very fast, zero latency DASD subsystem to the application.

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

Emulating a Shared DASD Device in Expanded Store on ES/9000 Class Systems

      Disclosed is a potential LIC feature designed to exploit the
large amounts of Expanded Storage available on ES/9000* class
systems.  This "Virtual Disk" feature enables applications to access
the system Expanded Storage utilizing any existing DASD software
written for any specific DASD device type (eg.  3380 or 3390 DASD
Subsystems).  Thus, exploitation of expanded storage by applications
does not require any special access method, or changes to the
applications.  The Virtual Disk can be dedicated to a single system
or the design can incorporate the option to share Virtual Disks
across multiple systems.  By designing the Virtual Disks to emulate a
DASD subsystem that is already known to software, it takes on the
appearance of a very fast, zero latency DASD subsystem to the
application.

      At initialization time, the operator may specify a portion of
Expanded Store that is to be used for the Virtual Disk.  The I/O
configuration is defined to contain a subchannel that is to be used
for all I/O operations against the Virtual Disk.  When an I/O
operation is executed against one of these subchannels, the channel
subsystem recognizes that the operation is actually against a portion
of Expanded Store and does not actually attempt to execute the
operation over a channel path.  Instead, the channel subsystem
branches to the Virtual Disk LIC routing that emulates the I/O
operation against the specified region of Expanded Store.

      Following system dependent initialization of the Virtual Disk
control blocks in storage, the channel subsystem is able to provide
emulation of the channel and DASD subsystems as follows:

The Control Blocks are:

o   Virtual Disk Control Block (VDCB).  The VDCB controls the overall
    Virtual Disk environment.
o   Track Map Table (TRKTBL).  The TRKTBL maps device tracks into the
    assigned region of Expanded Store.
o     Record Map Table (RECTBL).  The RECTBL maps device records onto
    the emulated tracks in Expanded Store.

The Emulation Services Provided are:

1.  A Virtual Channel appearance when an I/O operation is executed
    against a subchannel whose Virtu...