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

High Performance Cooperative Count Key Data/Fixed Block Conversion Mechanism

IP.com Disclosure Number: IPCOM000117143D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 161K

Publishing Venue

IBM

Related People

Ouchi, NK: AUTHOR [+2]

Abstract

Disclosed is a mechanism for CKD/Fixed Block conversion that permits a CKD process and Fixed Block process to execute in a cooperative, loosely coupled manner. Each process sees the buffer and the information from the other process in terms closely related to the operations that it executes rather than in terms of the "real" image of the buffer. The mechanism permits definition of the two processes in a simpler and more robust manner while still providing the opportunity for over-lapped operations and high performance.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 45% of the total text.

High Performance Cooperative Count Key Data/Fixed Block Conversion
Mechanism

      Disclosed is a mechanism for CKD/Fixed Block conversion that
permits a CKD process and Fixed Block process to execute in a
cooperative, loosely coupled manner.  Each process sees the buffer
and the information from the other process in terms closely related
to the operations that it executes rather than in terms of the "real"
image of the buffer.  The mechanism permits definition of the two
processes in a simpler and more robust manner while still providing
the opportunity for over-lapped operations and high performance.

      Two loosely coupled processes are used for Count Key Data
(CKD)/Fixed Block conversion.  Disclosed is a mechanism that
localizes information to each process to minimize coupling and
interaction so that simple, robust, high performance control
functions can be implemented.

      A CKD emulation storage system using fixed block devices is
constructed using a buffer and two processes: a Fixed Block process
that creates track images in the buffer, and a CKD process that
executes the variable length CKD read/write operations on the track
image.  To minimize opportunity for errors, these processes are
independent, loosely coupled, with a minimum of communication.  The
block structure of the storage system is illustrated in Fig. 1.
Illustrated in Fig. 2 is the view of the buffer as seen by each
process.  The CKD process views the buffer as a set of tracks where
each track is a seamless address space that has the characteristics
of the emulated CKD device.  The CKD process can then execute the
complex CKD command set independent of block boundaries.  The Fixed
Block process views the buffer as a set of block slots with blocks
having control information headers, error control fields, etc.  The
block view is far from seamless and contiguous.  In fact, the blocks
that form a "seamless" track may be scattered in the buffer and may
not all be there while the CKD process operates on the track image.
To achieve low response time, the CKD process must be able to start
as soon as the Fixed Block process has the first set of blocks for a
track in the buffer.  The Fixed Block process must continue to stage
tracks to stay ahead of the CKD process and destage blocks that have
been changed, written, by the CKD process after it has finished with
the track.  The CKD and Fixed Block processes are loosely coupled and
communicate through messages, as illustrated in Fig. 3.  The emulated
CKD DASD operations begin with a track request message from the CKD
process.  This may have some hints such as which part of the track
will be used, if the next sequential track will be used, etc.  The
Fixed Block process sends a message in response as soon as the first
blocks usable to the CKD process are in the buffer.  The CKD process
selects one of the tracks to activate (there may be several tracks in
the buffer ready for the CKD process).  The F...