Browse Prior Art Database

TZERO Sidefile Resource Management

IP.com Disclosure Number: IPCOM000112168D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 172K

Publishing Venue

IBM

Related People

Cohn, O: AUTHOR [+7]

Abstract

The TZERO design requires that the CU manage the sidefile in cooperation with the host. The CU sidefile is a logical partition of cache and must be managed as a limited resource. But since the host backup function has an intrinsic interest in how the sidefile is managed it must be made aware of the sidefile status, and it must be able to influence actions related to managing the sidefile. In addition, since the physical cache is shared between TZERO and the traditional cache file structure the sidefile management strategy must consider the affect that the sidefile has on the other users of the cache. The previous disclosure does not address the issue of managing the sidefile as a limited resource. It only describes the attention mechanism to indicate to the host that tracks have been staged to the sidefile.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 31% of the total text.

TZERO Sidefile Resource Management

      The TZERO design requires that the CU manage the sidefile in
cooperation with the host.  The CU sidefile is a logical partition of
cache and must be managed as a limited resource.  But since the host
backup function has an intrinsic interest in how the sidefile is
managed it must be made aware of the sidefile status, and it must be
able to influence actions related to managing the sidefile.  In
addition, since the physical cache is shared between TZERO and the
traditional cache file structure the sidefile management strategy
must consider the affect that the sidefile has on the other users of
the cache.  The previous disclosure does not address the issue of
managing the sidefile as a limited resource.  It only describes the
attention mechanism to indicate to the host that tracks have been
staged to the sidefile.

      TZERO describes how the sidefile is to be managed in
cooperation with the host.  The basic mechanism to manage the
sidefile is the establishment of a set of thresholds and actions
associated with each threshold.  The host influences the sidefile
management by setting session specific thresholds, and most
importantly it can relieve sidefile pressures by reading from the
sidefile.  The Control Unit's primary mechanism to relieve sidefile
pressures is de-establishing a session.  De-establishing a session
results in the freeing of sidefile tracks associated with the
session, and thus invalidating the session.  Since, it is undesirable
to invalidate a session, every effort is given to notify the host
prior to the de-establishment by sending attention messages.  In
addition, the sidefile reduces its impact on the other users of the
cache by allocating cache structures dynamically rather than
statically.

Five thresholds are described:

o   MAX% - MAX% defines the maximum cache utilization threshold
    expressed as a percent, e.g.50% cache utilization.  It is
    established for the sidefile as a whole.  The host cannot set
    this threshold.  When CU sidefile begins to consume MAX% of the
    total cache, then the session with the largest number of tracks
    will be de-established.  An attention message will also be sent
    to indicate that the session is de-established.

o   MIN% - MIN% defines the minimum cache utilization threshold
    expressed as percent of cache, e.g., 30% cache utilization.  It
    is established for the sidefile as a whole.  The host cannot set
    this threshold.  An attention message associated with the session
    with the largest number of tracks will be presented to the host
    when the CU sidefile begins to consume MIN% of the total cache.
    The host should then read from the sidefile.  MIN% must be
    sufficiently less than MAX% to allow the host enough time to
    begin reading from the sidefile.

o   STAGING_THROTTLE% - STAGING_THROTTLE% defines the cache
    utilization thresho...