Browse Prior Art Database

Volume Stacking Multiple Threshold Data Transfer Capacity Management

IP.com Disclosure Number: IPCOM000117550D
Original Publication Date: 1996-Mar-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 142K

Publishing Venue

IBM

Related People

Carlson, W: AUTHOR [+3]

Abstract

A method for managing limited data transfer capabilities in an automated volume stacking subsystem is disclosed. Multiple thresholds in the DASD stacking buffer are used to assign priorities to various volume stacking functions.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 38% of the total text.

Volume Stacking Multiple Threshold Data Transfer Capacity Management

      A method for managing limited data transfer capabilities in an
automated volume stacking subsystem is disclosed.  Multiple
thresholds in the DASD stacking buffer are used to assign priorities
to various volume stacking functions.

      An automated volume stacking subsystem uses a disk drive to
buffer data between the drives and the host computer.  When data is
created or modified in the buffer, it must be dumped onto a
cartridge. When data is dumped onto the cartridge, the original copy
will be kept  in the buffer as long as feasible to allow buffer
"hits" when that data  is requested again.  The buffer dump process
will be managed based upon  the aggregate size of all the data that
has not yet been dumped.

      If an automated volume stacking subsystem has limitations on
the data transfer bandwidth it has between the buffer and the drives,
it must be managed.  If, for example, the subsystem can only support
data transfer to two drives simultaneously, and more than two drives
are loaded, the data transfer capacity must be allocated between the
drives.  There are three different types of cartridges that can be
loaded in the drives:
  o  Specific Mounts - These cartridges contain volumes that have
been
      specifically requested to satisfy host mount commands.
  o  Reclaim cartridges - These cartridges contain volumes that are
      being "reclaimed" to create new dump cartridges.
  o  Dump cartridges - These cartridges contain data that is being
      spooled off the buffer.

      This disclosure addresses the priority of the dump cartridge
relative to the reclaim and specific mounts.  Since there is (in this
example) only enough bandwidth to support two drives simultaneously,
this disclosure addresses the first two dump cartridges (called Dump
#1, and Dump #2.  If only one dump cartridge is loaded, it is Dump
#1).

      The relative priority of the dump cartridges can be managed
using multiple thresholds as illustrated in the following diagram
(capacity not to scale).

      The rules for use of these thresholds is as follows.  If the
total amount of data not dumped is:
  o   Less than "Dump #1 Load Threshold" and greater than or equal to
       "Empty Buffer"
          If
      - Dump #1 cartridge is loaded
          Transfer data to Dump #1 if data transfer resources are
         available after servicing all loaded Specific Mounts and
         Reclaim Cartridges.
      - Dump #1 cartridge is not loaded
          Do nothing
      - Dump #2 cartridge is loaded (by definition Dump #1 is already
         loaded)
          Transfer data to Dump #2 if data transfer resources are
         available after servicing all loaded Specific Mounts,
Reclaim
         Cartridges and Dump #1.
      - Dump #2 cartridg...