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Performance Improvements through the use of Multi-Channel Command Word

IP.com Disclosure Number: IPCOM000116394D
Original Publication Date: 1995-Sep-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 64K

Publishing Venue

IBM

Related People

Beardsley, BC: AUTHOR [+3]

Abstract

A new method is being developed to allow a back-up copy of a DASD volume to be created on a device located kilometers from the primary DASD volume. This method uses control unit to control unit communication across ESCON interfaces to accomplish the transfer of data (records) from the primary control unit to the secondary control unit. This copy is synchronous with the I/O to the primary device; i.e., the completion of the primary I/O is not signalled until the data has been copied to the secondary control unit.

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

Performance Improvements through the use of Multi-Channel Command Word

      A new method is being developed to allow a back-up copy of a
DASD volume to be created on a device located kilometers from the
primary DASD volume.  This method uses control unit to control unit
communication across ESCON interfaces to accomplish the transfer of
data (records) from the primary control unit to the secondary control
unit.  This copy is synchronous with the I/O to the primary device;
i.e., the completion of the primary I/O is not signalled until the
data has been copied to the secondary control unit.

      In order to minimize the additional overheads introduced by the
remote copy a new method is needed to insure the fastest possible
data transfer between the primary and secondary control unit.  This
is for both the synchronous update of the secondary DASD and the
initial copy of data from the primary to secondary DASD.  The current
method of transferring data to a DASD control unit/device is with a
series of commands such as:
  o  Define Extent
  o  Locate Record
  o  Write
  o  Write

Two types of overheads are inherent with the above command chain.
They are (1) control unit overheads involved with processing each
command and (2) channel overheads related to the number of frame
transfers required to complete the operation.  The channel overheads
are also significantly affected by the distance between the primary
and secondary control units.

      While the solution is explained in terms of a remote copy
environment it applies equally to a host to control unit environment.

      Through the use...