Browse Prior Art Database

Non-Disruptive Global Status Track Expansion

IP.com Disclosure Number: IPCOM000114023D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 121K

Publishing Venue

IBM

Related People

Kukula, DA: AUTHOR [+2]

Abstract

The global subsystem status contains the status of subsystem cache and Non-Volatile Storage (NVS) as well as caching, DASD fast write and dual copy status for each device in the subsystem. In order to add new status information for the subsystem or device and to add more devices, additional information is required on the global status track. This additional information can be added non-disruptively, with the current status preserved, by setting one of the unused bits in the existing record to indicate an additional record exists that contains new status.

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This is the abbreviated version, containing approximately 52% of the total text.

Non-Disruptive Global Status Track Expansion

      The global subsystem status contains the status of subsystem
cache and Non-Volatile Storage (NVS) as well as caching, DASD fast
write and dual copy status for each device in the subsystem.  In
order to add new status information for the subsystem or device and
to add more devices, additional information is required on the global
status track.  This additional information can be added
non-disruptively, with the current status preserved, by setting one
of the unused bits in the existing record to indicate an additional
record exists that contains new status.

      The global subsystem status is used to keep the state of the
sub- system and devices when the control unit is powered off.  This
enables any modified data that exists during a power off to be
written to the appropriate devices when power is restored so that
data integrity can be maintained.

      The status track manager creates, maintains, and stores the
global subsystem status.  The global subsystem status contains the
state of the cache and NVS in the subsystem as well as status for
each device.  The device status reflects the caching, DASD fast write
and dual copy status for each device in the subsystem.  A status
track must be written on the device support cylinder of a device
before that device can be accessed by the subsystem.  The status
track contains the ID portion which is four bytes, comprised of the
two byte subsystem ID, one byte Logical Device Address (LDA), and one
unused byte.  Two devices on the subsystem, the global status
devices, also contain the global subsystem status.  Present status
track support writes two 512 byte records, one and two, the second
being a duplicate of the first.

      On Initial Microcode Load (IML), the global subsystem status is
generated in Joint Array Structure (JAS) and written to the global
status devices.  The global subsystem status is maintained in JAS and
written down to both of the global status devices whenever there is a
change in the global subsystem status.  On subsequent IMLs, the
global subsystem status is read from the global status devices and
stored in JAS.

      Currently the 512 byte records consists of the global portion
of the status and the status for each device.  In order to expand the
number of bytes for the subsystem portion, the number of bytes per
device in the device status portion or the number of devices, the
track must be reformatted.  Any format changes must be compatible
between old and new levels of microcode so that a different level of
microcode (uplevel or downlevel) can be installed concurrently and
still maintain the subsystem and device statu...