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VSAM Key Sequential Data Sets Striped Data Disclosure Number: IPCOM000119151D
Original Publication Date: 1997-Dec-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 84K

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Thompson, DK: AUTHOR


Disclosed is a method for the Format of Data for Striped VSAM Key Sequential Data Sets (KSDS).

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This is the abbreviated version, containing approximately 53% of the total text.

VSAM Key Sequential Data Sets Striped Data

      Disclosed is a method for the Format of Data for Striped VSAM
Key Sequential Data Sets (KSDS).

      In the Figure, a particular set of contiguous CIs represent a
set of stripes.  A set of these sets will represent a Control Area
(CA).  The value 's' represents the particular stripe set in which we
are interested.  Values of interest are obtained in the following
  o  CI number - the RBA for the CI wanted divided by CI size.
  o  Value 's' - the stripe set for the requested CI.
     This is obtained by dividing the CI number by the number of
  o  Stripe set - one set of CIs which represent all stripes.
     The number of CIs in a set is equal to the number of stripes,
      and the CI is on the stripe boundary for the first stripe.
  o  Device - determined from the EDB entry.
  o  Location of CI on device - determined from the EDB entry.

      Prior art required a control area for a VSAM KSDS to be
maintained on a single device.  The direction being taken for
striping spreads the control area over more than one device allowing
control intervals to be read simultaneously from the different
devices for one  control area.

      VSAM KSDS Striping allows control intervals of data for the
base data component to be transferred from devices through control
units to the central processor at speeds which exceed the capability
of a single channel path.  The transfer rate which may be achieved is
based on the amount of data being transferred from a single device,
and the items which affect the transfer, such as seek time,
rotational delay,  and activity in the control unit which may affect
cache usage. Queues  in MVS IOS processing for the device may also
cause response to be delayed.  The maximum transfer rate which may be
achieved is limited by  the slowest device involved in the
Input/Output (I/O) request; this may  be a device which has a logical
mapping that is equivalent to other devices in use or the data may be
in some but not all caches.

      The capability to achieve improved data transfer using striping
requires the sequential transfer of data; with VSAM this is
accomplished by using the sequential option code for the request.
Even specifying sequential may not be sufficient if another request
has also specified  sequential for the RPL.  Direct processing, on
the other hand, retrieves  one...