Browse Prior Art Database

Servicing of Incorrect Load Source Disk Data Level

IP.com Disclosure Number: IPCOM000102654D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 8 page(s) / 269K

Publishing Venue

IBM

Related People

Effle, JS: AUTHOR [+5]

Abstract

Described is a system which determines whether or not the load source used to initialize the system is at the correct level. If the load source has incorrect data, service is still allowed to be performed on the system while informing the user of the incorrect data and preventing improper repair actions.

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

Servicing of Incorrect Load Source Disk Data Level

       Described is a system which determines whether or not the
load source used to initialize the system is at the correct level.
If the load source has incorrect data, service is still allowed to be
performed on the system while informing the user of the incorrect
data and preventing improper repair actions.

      The following items are discussed:
1.  Determining the correct load source disk device of a computer
system.
2.  Blocking access to the computer system for use other than service
if an incorrect load source disk device has been used to initialize
the system.

      Fig. 1 is an illustration of how identifying data is kept on a
disk device.  The identifying data is used in the implementation to
determine if the given disk device is a load source disk device
(capable of being used to initialize the system), and if all disk
devices contain the same level of data.

      The system checks for clues that multiple load sources exist on
the system.  The clues are:
-  Multiple disk units report that claim to be load sources.
-  The IPL number is higher on some disk units than on the IPL load
source.  The IPL number is incremented for each IPL and is kept on
all configured disk units.
-  The load source I/O address stored in the nonvolatile storage in
the main processor does not match the current IPL load source.
-  For a mirrored load source, the mirrored load source state is
unknown or back level.

      When any of these clues exist, the system does a complete
evaluation to determine the correct level load source.  Usually none
of these clues exist; thus, the time to do the evaluation, which
requires many disk operations, is usually avoided.  The correct level
load source is the most recent load source that is for this system.
(Might be the IPL load source).  The system first finds the disk unit
with the most recent disk device configuration table (DCT). The DCT
identifies the load source.  The factors used to evaluate and
determine the most recent DCT for this system are:
-  System Serial Number.  All configured disk units contain a system
serial number.  Disk units with a different system serial number are
ignored because they really belong to a different "system".
-  Time Stamps.  All configured disk units contain time stamps.  The
time stamp is updated when a global disk device configuration change
is made.  The time stamp is a tie-breaker when the system serial
numbers are the same from different disk units. Thus, a disk unit
with a more recent time stamp contains a more recent DCT which may
identify a more recent load source.
-  Unit Sequence Numbers.  Each configured disk unit has a unit
sequence number.  The unit sequence number is incremented for disk
device configuration changes and state changes.  The unit sequence
number is only changed on the device being reconfigured. The DCT
contains the unit sequence numbers for all configu...