Browse Prior Art Database

Complete Track Indication for Increased Count Key Data Emulation Performance

IP.com Disclosure Number: IPCOM000115652D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 96K

Publishing Venue

IBM

Related People

Ng, C: AUTHOR [+3]

Abstract

Count Key Data (CKD) emulation on fixed block devices and arrays require that write operations stage portions of the track image to a semiconductor buffer so that the affected portion of the track image can be changed and then destaged back to the devices. This operation is illustrated in Fig. 1. There is art that maps the CKD blocks to the fixed block so that complete blocks are changed to avoid staging of blocks. There is art that defers the staging of the blocks by saving indication of the track format so that the data are accepted as a "write hit" even though the image of the data are still on the fixed block devices. Disclosed is an indicator of a class of CKD operations so that the track image need not be staged; the track image is created in the buffer and then destaged directly to the devices.

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Complete Track Indication for Increased Count Key Data Emulation
Performance

      Count Key Data (CKD) emulation on fixed block devices and
arrays require that write operations stage portions of the track
image to a semiconductor buffer so that the affected portion of the
track image can be changed and then destaged back to the devices.
This operation is illustrated in Fig. 1.  There is art that maps the
CKD blocks to the fixed block so that complete blocks are changed to
avoid staging of blocks.  There is art that defers the staging of the
blocks by saving indication of the track format so that the data are
accepted as a "write hit" even though the image of the data are still
on the fixed block devices.  Disclosed is an indicator of a class of
CKD operations so that the track image need not be staged; the track
image is created in the buffer and then destaged directly to the
devices.

      CKD requires that the track image be formatted to create the
variable length key and data fields and the control blocks called
count fields.  The format operation can begin after any valid record
on the track and alters the balance of the track to INDEX.  Data that
was on that area of track image will be destroyed thus the track
image need not be staged.  The complete track operation is
illustrated in Fig. 2.  Indication of a full track format operation
is set in the Extended Count Key Data (ECKD) Define Extent - Locate
Channel Command Words (CCW).

      Track formatting may be thought to be done only when a track is
assigned to a new use and an infrequent operation.  However, there
are two major high performance applications that can take advantage
of the characteristics of the format operation: SORT and IMS.  SORT
can use DASD in a full track mode where the SORT Works write complete
tracks using a format number of records using format write.  The data
are read record by record and not necessarily as a complete track.
The SORT full track mode sets a specified bit in the ECKD Define
Extent/Locate, DE/L, commands to indicate that the tracks will be
written using a format that starts after a standard RO count field.
The balance of the CCW chain is a set of Write CKD Format operations
that format and write the SORT Works data.  The disclose...