Browse Prior Art Database

Track Predictive Range for ECKD Domains

IP.com Disclosure Number: IPCOM000112336D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Cohn, O: AUTHOR [+7]

Abstract

A frequent problem for Disk Drive Control Units is to predict the range of tracks that a I/O chain may access. This prediction may be used to perform some operation for the channel I/O chain while the chain is disconnected from the control unit. When the Control Unit completes its work it indicates to the channel to reconnect. The channel may then continue its I/O chain. For instance, it may be desirable to stage or destage tracks from the control unit's cache in order to reduce channel connect time and the overhead for connect/reconnect of a given chain. This invention describes an algorithm that predicts the range of tracks that a channel program running ECKD domains may access.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 74% of the total text.

Track Predictive Range for ECKD Domains

      A frequent problem for Disk Drive Control Units is to predict
the range of tracks that a I/O chain may access.  This prediction may
be used to perform some operation for the channel I/O chain while the
chain is disconnected from the control unit.  When the Control Unit
completes its work it indicates to the channel to reconnect.  The
channel may then continue its I/O chain.  For instance, it may be
desirable to stage or destage tracks from the control unit's cache in
order to reduce channel connect time and the overhead for
connect/reconnect of a given chain.  This invention describes an
algorithm that predicts the range of tracks that a channel program
running ECKD domains may access.

      Technical Description - Ideally the range of the tracks
included in the prediction would span all of the tracks to be
accessed, but it would not include any tracks that would not be
accessed.  In fact, it is impossible to derive an exact prediction
without storing the format of each track since all information is not
available at the initiation of an ECKD domain and there is no
certainty that the domain will complete successfully.  An exact
prediction is hampered by the fact that track capacity may be
under-utilized and the control commands, Define Extent and Locate,
that prefix all ECKD domains do not require the channel to supply
exact information about the intent of the domain.  For instance,
record block size in the Defi...