Browse Prior Art Database

Long Busy Conditions

IP.com Disclosure Number: IPCOM000100281D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 86K

Publishing Venue

IBM

Related People

Beardsley, BC: AUTHOR [+4]

Abstract

In a complex Storage Control environment such as the one associated with the IBM 3900 Model 3, certain activities result in Storage Control entering into a dedicated mode of operation. A dedicated mode of operation is used to minimized integrity exposures. Examples of when this mode is used are cache and non- volatile storage initialization and cache and non-volatile storage failures. If a failure occurs, the modified data that is in the non-failing unit is written to permanent storage.

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

Long Busy Conditions

       In a complex Storage Control environment such as the one
associated with the IBM 3900 Model 3, certain activities result in
Storage Control entering into a dedicated mode of operation.  A
dedicated mode of operation is used to minimized integrity exposures.
 Examples of when this mode is used are cache and non- volatile
storage initialization and cache and non-volatile storage failures.
If a failure occurs, the modified data that is in the non-failing
unit is written to permanent storage.

      As a result of being in this dedicated mode of operation the
Storage Control is busy and can not accept work from external
sources.  Since this dedicated mode may exceed the limits of the
associated operating systems missing interrupt handler, some form of
special handling is required.  The special handling by the operating
system is triggered by the presentation of special sense by the IBM
3990 Model 3 Storage Control.

      There are two types of busy status, device busy ('10'x, Busy),
and control unit busy ('50'X, Status Modifier and Busy).  Busy status
is presented to the host operating system to indicate that the
requested work can not be performed due to the unavailability of
resources.  Device busy is presented when the device is not
available.  Control unit busy is present when the control unit that
is used to attach the channel to the device is busy.  In either case,
when the host operating system receives this status, it notes the
fact and waits for status from the subsystem that it is available to
do the requested work.  If the operating system in the host does not
receive this status, it assumes that the device is not operational.
This process is known as missing interrupt handling.

      There are a number of situations in which the IBM 3990 Model 3
Storage Control may be busy for periods that may exceed the limits
established by various operating systems for missing interrupts.
Most of these conditions are associated with the extended functions
provided by the IBM 3990 Model 3 Storage Control.  Some of the
activities which result in this condition are as follows.
   - Emergency destage from th...